I am speaking for myself, but there are a few reasons why I don't play much on that server. The server is at the point where everyone joins the same games, even as just a watcher if they aren't playing, which leaves not many other playing options for others. And the games that everyone joins is always for top tier players. I am not at the calibre where I can compete with the top players, due to not playing in like 10 years, so I would just be letting teammates down by being useless. Once in a while there's a new player, but I am not new either, so it would not be fair to compete against noobs. I am stuck in the middle somewhere, and it is difficult to find games around my skill level.
Also, the attitude of the majority of players is a bit aggressive, which can be very unwelcoming, especially to newer players. I personally don't get offended by the aggression, but it does affect my willingness to join games just because, for me, it comes across as people taking the game too serious and caring too much about winning. I don't feel competitive enough to fill the slot of an ally for people that want to win. Teams would just be imbalanced in favor of my opponents, and a handicap to my partner. Would be fine if everyone played for fun and didn't care too much, but I feel pressured to find a way to be competitive.
I do want to get better at the game so I can play with the top players again, but I feel like I need to find more people around my level to compete with until then. Thankfully there are a couple other servers out there with players around my level, which I've been having a blast with, but the RU server, truthfully, just feels unwelcoming for me. Would be nice if we were able to make games more inclusive of all skill levels, but I understand that is a tough thing to do.