Because the two documents are answering different questions. “Best project tracker for a five-person agency” is a request for a set: several named candidates, each with a reason attached and a boundary where it stops being the right pick. A vendor page is a document about one entity, and its job is to end the comparison rather than conduct it. Retrieval scores documents against the query as issued, so a page that already has the shape of the answer wins the match on structure, before anything about quality or trust is weighed.
Read the failure from the engine’s side and it stops looking like a verdict on your writing. To build a shortlist out of single-vendor pages, a system has to find each candidate separately, decide which candidates belong in the set at all, and construct the comparison itself from documents each written to win it. One roundup hands over all three jobs pre-solved, and nothing in that requires the roundup to be independent, well written, or even current.
The one systematic review of this literature grades the same boundary: it rates “query–document relevance and context position are major determinants” at high confidence, and a white-hat intervention durably improving discoverability across engines at low.3 Relevance to the issued query is the part of this system with strong evidence behind it, and relevance is exactly where a single-vendor page is structurally short.