You're counting on the entire opposing team being dumb. If I start at A and we can't get C on initial push but at some point in the game my spawn flips I don't go near B. I try my best to clear out the area around C and hang near the back until the rest of my team starts spawning there. One person who knows the importance of the spawn locations on that map will screw you royally unless you can kill them and reflip spawns. B isn't the important point to control... C is.