They want to get recommendations just good enough to keep you hooked. If they show you just the objectively best, you would instantly know after seeing the best ones, that the rest of the catalogue is worse and worse.

This is how Netflix was in the beginning. I actually unsubscribed for a while for yhis reason. Now I'm as hooked as ever, there might still be a few good ones out there - I just need to keep scrolling for a few hours. /s