Efficacy plays a role in this effect, but so does unintuitive connections between search terms and results. "Google-fu" used to be a somewhat solid "science" but now small query differences can yield unpredictable effects on results, and the likelihood of remembering the exact query that yielded the desired result is low.
Tangent, I was searching for 3mm spherical magnets last night and literally every retailer's search is total garbage and delivered any kind of magnet you can imagine while occasionally sprinkling in things that were vaguely related to "3mm spherical magnets"
I don't understand how it's useful to anyone, even the companies. I just leave without buying things so why would their searches not just search for the specific thing that I ask for?
I haven't ever figured out why search is so hard for so many websites, including some that I've worked on. Even using third parties (like Keyoti) I've had trouble. In one case I solved a lot of issues with Elastic, but it's sort of overkill for 90% of website use cases.
It's also related to the fact that since ~2010, the quality/efficacy of "search" has gone downhill and you'll never find anything again.