When I lived in London, and used buses fairly regularly, I started thinking about ways to improve the service and stop bunching. I considered the reason stated here, and some of the solutions, but later realised that the root cause was that the drivers liked to stop and chat and perhaps play cards with each other at the (presumably unsupervised) "bus station" at the far end of the route. Once I'd observed 3 of them waiting for each other, chatting, and then all leaving at once on the same route, my interest in trying to think of ways to fix the problem waned.