It's a pity. There is a long list of great maps that I've never seen being played.
I'd say the problem is in both sides. Server admins like to add maps that most players already know and when there is no players around have bots running in those (there is a lot of maps that don't have anykind of bot files(.waypoints, etc.)) so their servers seem to be "more popular" and I get it, no one enjoy to just run around in an empty server waiting other players to join in (I do). Also they are too afraid to try something new, same as most of the players. It's easier (and for some, more fun) to play same maps again and again (when you probably know them better than your own pockets) than try to learn and experience something new.