One of the reasons for this is SurvivorBots, despite their relatively solid behavior overall, can occasionally get stuck on an obstacle or trying to decide betw

One of the reasons for this is SurvivorBots, despite their relatively solid behavior overall, can occasionally get stuck on an obstacle or trying to decide between divergent priorities (follow the others or grab a powerup? They can get stuck in a "dancing loop" where they shuffle a couple steps one way and then the other.) It's important in L4D to require players to pay attention to their teammates, but it's also important to maintain the "fun" aspects of the game. It's one thing if the AI gets behind because they're being attacked and the player is doing a bad job of protecting them; it's entirely different if the AI gets behind because its algorithm sometimes gets hung up (and it's not fun for the player to have to try to solve pathing glitches!)