I had a job interview for game tester at EA a month ago (got hired by the way.. start work in a couple weeks), and when they asked me "Name one thing you'd like to see improved in BF2", I suggested just what you suggested here. The interview dudes seemed to like the idea, but I don't think they were in control of such matters.
It's a good idea because it's basically free work and money for EA. Gamers create new maps, EA slaps 'em in, and gamers tell their buddies how the game is always fresh and cool. Buddies go out and buy BF2, and the cycle continues. I guess EA wants to keep the well dry so you go out and buy the expansions/boosters. But that seems odd since great mods are bound to come out eventually anyway..
Adventures of a video game mercenary
http://virtualmerc.blogspot.com