With the right search query, one can frequently find exactly what they are looking for very quickly. In some sense having a dumber search engine than Google is advantageous here as you won't become dependent on the "magic" of the search engine and will have to craft a good search strategy.
The most valuable technical feature of the internal search tools (PE2E Search or EAST) was speed, not anything fancy. I imagine this was the motivation: If the results can't easily be ranked (and they couldn't in my experience), make handling a ton of results as easy as possible. That's what the USPTO did.
You could "flip" through documents quickly using only the keyboard, and if what you were looking for was easily visible in a drawing then this usually was the best approach. For text they had a good way to show what you were looking for in context. I'd love to see a similar setup for web search but I don't think it would appeal to most, so it probably won't happen.
AI/ML based search tools were interesting but usually not helpful. I'd always try at least some of them. I think the main limitation for these in my technology area (mostly water heaters and ventilation) was that they didn't look at the drawings at all, just the text and citations. That's missing a lot. (When they were helpful they did save a lot of time.)