I think it’s more that not every comment gets upvoted after there is quite a few.
Early comments get voted on by merit. Once there is a few comments that have sufficient upvotes and replies, they become their own ecosystem.
If I’m in the comments of a popular post, I might upvote the first few top level comments I see as all make a good point. The fifth might make the best point and deserve to be higher, but alas, it only gets one upvote. By the time I get to the sixth, it’s just saying the same thing differently, no upvote needed. Seventh is interesting, so upvote, but it’s getting boring now. I don’t read further comments.
Other people stop at comment 10. Others stop at 4. So the first few get magnified, the rest struggle for the same level of attention and eyeballs. But it’s not a competition. So if the discussion is good, who cares. The 10th discussion might be the best because all the people with short attention spans, like me, aren’t there.
Yes, if you know about that community. However, by browsing the all feeds of multiple instances, you come across communities you weren’t aware of and can subscribe to on any of the instances you have an account on. Assuming, of course, they all federate.