It's kind of like comfort food. CS has variants like gungame and deathmatch, you can have modded servers with alternate damage, fire rate, recoil, low gravity, or even mods that change it entirely and turn it into a zombie horror game or an RPG. And those are fun, but ultimately I want to return to the game I know and love.

Chess is the obvious comparison, but also so is any major sport. There hasn't been anything significantly changed about Soccer, Basketball, Baseball, and so on, in a long time as well and most people don't have issues with that. Once you eliminate changing the game rules you're left with only trying to develop your own personal skills.

I don't know anything about CS, but in the Starcraft scene the meta is always evolving because new maps come into rotation that push players to develop new strategies. I guess LoL does something similar by adding new characters.