The divergence comes from what the hierarchy is actually doing in each vertical, not from the URL string itself. Google has stated plainly, including through John Mueller in multiple public comments, that URL structure carries very little direct ranking weight on its own; a folder path like /category/subcategory/item is not read by Google’s systems as a trust or relevance signal in the way a title tag or heading might be. What differs between verticals isn’t the URL, it’s whether the hierarchy that a nested structure implies is doing real work elsewhere: organizing internal links so topical authority flows to the right pages, or establishing context that helps both users and ranking systems understand what a page is about before they’ve read a word of its content. Flatten a structure where that hierarchical grouping matters, and you lose the thing the URL nesting was a side effect of. Flatten one where it doesn’t, and you lose nothing, and often gain simplicity.
Where flat structures win: independent-relevance verticals
In verticals like ecommerce product listings, job postings, or individual reference entries (a specific product model, a specific address, a specific transaction record), each page’s ranking potential is largely self-contained. A product page competes on its own merits for its own product-specific queries; a buyer searching for a specific SKU or model number doesn’t benefit from, and doesn’t need, three levels of category context to understand what the page is. In these cases, nesting a URL under /electronics/audio/headphones/model-x doesn’t add relevance the page didn’t already have from its own title, content, and structured data, and it adds a structural cost: every additional directory level is, in a typical site architecture, an additional hop away from the homepage or other high-authority entry points in terms of internal link depth, unless the site owner deliberately compensates with strong cross-linking.
Crawl depth is the mechanistic link here, and it is something Google has discussed directly: pages that are many clicks away from a site’s most-linked pages tend to receive less frequent crawling and can be slower to have signals recognized, not because depth is itself a ranking factor, but because internal link equity and crawl priority both tend to concentrate on shallower, more heavily-linked pages in typical site structures. A flat structure, where product-level pages sit close to the root or close to a single index page that links to all of them, keeps that internal linking distance short by default. That’s the actual mechanism, not the URL string, but a flat structure is highly correlated with shallow linking because it’s the natural output of a flat information architecture, whereas nested URLs are often (though not always) a symptom of a nested internal linking structure with more hops between the homepage and the leaf pages.
Where nested structures win: taxonomy-dependent verticals
In verticals where the category itself is part of what establishes the page’s relevance and trust, legal content organized by practice area and jurisdiction, medical content organized by condition category and specialty, or any domain where users and evaluators alike expect a piece of specific information to sit within a demonstrated broader competence, flattening the structure removes real signal, not just a cosmetic detail. A page about a specific legal question benefits from being demonstrably part of a well-organized cluster on that practice area, because the hierarchy is what lets breadcrumbs, category pages, and internal links establish topical grouping: this page belongs to this practice area, which belongs to this broader legal category, and the site has evident depth and organization across that whole space.
This connects directly to how Google’s quality systems evaluate expertise and trustworthiness contextually rather than page-by-page in isolation. A single isolated page making a legal or medical claim reads differently, to both users and evaluators, than the same page sitting visibly within a well-organized topical cluster with clear categorical relationships to related pages. Nested URLs aren’t the mechanism that creates this effect directly, again per Google’s own statements about URL structure being a weak signal, but nested hierarchies are usually built alongside the actual mechanisms that do matter: breadcrumb navigation reinforcing the categorical relationship, category-level hub pages that concentrate internal links into their child pages, and a URL path that (even if not read as a ranking signal itself) reflects and reinforces an information architecture that a flattened structure would have to recreate through other means, or lose entirely.
Flatten this kind of vertical without preserving the underlying breadcrumb and internal-linking hierarchy, and you don’t just change a URL, you remove the categorical grouping that was doing real relevance and trust work, and you frequently see exactly this fail: individual pages that previously benefited from sitting inside a demonstrated topical cluster start performing as isolated, unaffiliated pages instead, with weaker internal link equity flow and no categorical context signal to lean on.
The practical implication: it’s an architecture decision, not a URL decision
This is not a documented Google ranking rule about flat versus nested URLs, and treating it as one is the wrong takeaway; no such rule exists, and Google’s own statements point the opposite direction, toward URL structure being a weak signal in isolation. The real decision is whether your vertical depends on hierarchical grouping to establish relevance and trust (taxonomy-dependent), in which case you need to preserve or rebuild that hierarchy’s actual mechanisms, breadcrumbs, category hub pages, deliberate internal linking between related items, regardless of whether the URL itself is flat or nested, or whether each page’s relevance is fundamentally self-contained (independent-relevance), in which case minimizing link depth and structural complexity by flattening is a legitimate simplification with little to lose.
The practical test for any programmatic page set is to ask what would actually change if you flattened the URLs while deliberately keeping the breadcrumbs, category pages, and internal link clusters intact. If the answer is “nothing meaningful,” the vertical is in the independent-relevance category and flat URLs are a safe, often beneficial simplification. If the answer is “the categorical grouping and internal link equity flow would have to be entirely rebuilt through some other mechanism,” the vertical depends on the hierarchy itself, and flattening the URL without preserving that underlying structure is what produces the catastrophic failure, not the URL format in isolation.
Hypothetically, imagine two site migrations happening in the same quarter. “Example Parts Store” flattens its product URLs from /category/subcategory/brand/part-12345 to /part-12345, but keeps every product close to a single root index page with strong internal linking; let’s say performance holds steady or improves slightly, since each product page’s relevance was always self-contained. “Example Legal Guide,” covering multiple practice areas, makes the same flattening change to its URLs but, in this hypothetical, also removes the breadcrumb trail and the practice-area hub pages during the same redesign. Its individual pages, previously reinforced by sitting inside a visible topical cluster, start performing as isolated pages instead. The difference in outcome, in this hypothetical pair, traces back to whether the underlying hierarchy mechanisms were preserved, not to the URL format itself.
