I can't think of a better rationale for the ubiquitous worsening of local search than increasing ignorance of comp sci fundamentals.

There's no reason a senior at undergrad level shouldn't be able to write an efficient, fast, deterministic, precomputed search function.

... and yet, professional developers at major companies seem completely incapable.

Minimum acceptance criteria for any proposed shipping search feature should be "There is no file / object in the local system that fails to show up if you type its visible name" ffs.