Because most of them were thrown together by EA last minute so they were full of bugs and problems.
Most of the maps that I did work on had a ton of problems. I did lots of work to fix tons of problems not only on maps, but in the game itself.
The game was only supposed to be released with like 5 multiplayer maps, but last minute they decided to make it as many maps as possible so they were just thrown together and they hoped that the patches would fix them... Then they only released 2 patches.