I'm not an official answerer, but let me take a crack at it:
A map rotation is the moment where most people take the opportunity to leave for another server. We want to keep people around, having fun, for as long as possible. So we try to reduce map changes.
Also, most of our servers are 24 hour map servers; having those "map switching" back to the same map over and over again get old, real fast.
The team balancer should be kicking in, but, yeah, I know, it's a bit annoying to be stuck with the "losing team," but I just take that as motivation to play my best and eventually squish the other team.
Here's some pessimism: they type of people who MUST be on the winning side will quit and rejoin, go to spec, and otherwise try to avoid teamswitching. 'Course, if an admin catches them doing that, they're asked to stop; it ruins the game balance. But in general, trying to force people to be nice and teamswitch to the "losing team" rarely works
But there's a plus side: in TF2, the "losing side" is usually losing because there's 3-5 lone wolfs piddlefarting around the server on your side, not supporting the team. Now, these people also generally hate being rolled, EVEN THOUGH THEY ARE NOT CONTRIBUTING. So what happens? One or two rolls, they leave, and we pull the one-armed-player-bandit to get a new player.
I've been on dustbowl, rolled 4-5 times, the team finally decides that they can't "vote themselves" a win, but actually have to produce it themselves, and we suddenly roll the other side 2-3 times, because they got complacent
