Because the good guys are too busy being doormats for the *******.
In the movies? In real life it is because the Bad guys can be random. They have many more choices that the good guys. They don't have to follow any rules. Take the Tet Offense in the Vietnam War. They attacked during a holiday/cease fire. I was told by a Iraq War veteran that the enemy would engage in a surprise attack and as soon as you got them on the run, they would give up. It leaves the good guys feeling like they can never go "toe to toe" with the enemy because they don't play by our rules. The minute you are in a place to "beat the **** out of them" they give up.
Are you a bad guy??