it wouldn't have been so popular back in TF2's heyday
TF2 then and TF2 now are two different things. Back then, people stuck to their communities and didn't play anything else. That was during the quickplay era. Nowadays, we've got less and less people playing community servers, and they don't have a high level of loyalty to any specific community, only to a specific server at most.
(plus several server owners such as Uncle Dane wouldn't be maintaining full servers consistently).
Uncletopia is a special case, as that community has the backing of a creator behind it.
The game just isn't fun for anyone when hits don't register due to jittery hitboxes.
I can understand the sentiment, but based on my own surveys, players pick fuller servers over lower ping. One big example I can give is the US class wars server - we've got an identical one in europe, but it's constantly dead, and most europeans play on the US region one instead, as that has the more reliable playerbase.