In my case as can't speak for anyone else, but I kept planet scavenging because it became my white whale.
It was no longer about how can I get the 6 or 12 or whatever number of yttrium I'd need to equip my small fleet of ships with rank 4 FSD *my current Felicity rank.
It became a massive puzzle re: lack of metallic meteorite rocks even spawning. Some people are confusing my issue as 'can't find yttrium planets' or 'not getting any yttrium'. That is not it at all.
I may very well complain, later, about the rarity of yttrium - or not. But I have zero way to know that personally at moment because my issue is not getting yttrium out of metallic meteorites - it is finding MM on surfaces of known planets in the first place. That is my white whale at this point. The more I went without finding barely any MM at all, and after I was sure it was not due to lack of info re: what the scans look like, how to optimize looking for them, etc - I just kept at it.
If I just wanted yttrium, yes - I'd go do the barnacles thing. But I gave it a good long shot to SRV scavenge to see if like any case of odds - I was having a long run of bad and hopefully was due for some good. Unfortunately not.
But as I said, the thread was mainly to relate some disappointment that one of the prime activities I bought the Horizons expansion for, is something I now associate with such bad taste due to fruitless searching, that I don't even want to drive one at all, whether I am scavenging or not.