Indeed. You can do all sorts of complicated analysis of where, when, and how frequently buses bunch. But the explanation is very simple - like magnets, buses attract each other, in a positive feedback loop. As long as the waiting time at each bus stop depends on the number of passengers that have to get on and off, then buses will always bunch. This is caused by the bus schedule being tight, so the bus has to keep on driving to stay on time. The problem will be worse the more frequent the service is.

The solution is also very simple. Stop the waiting time at each bus stop depending on the number of passengers that get on or off. Slacken the timetable, so that every few stops the bus waits for a minute to match the schedule.

On bus routes with very frequent service, for instance every 10 minutes or more frequent, there is no longer really any need to have a timetable - it will be a bigger win for the customer to just make sure the buses don't bunch than it is to actually publish a timetable. In this case, you may want to implement a negative feedback loop based on vehicle tracking. Most buses are remotely tracked now anyway, so it shouldn't be too hard to return a signal to each bus saying either "carry on as normal" or "you're too close to the bus in front, wait a bit at the next stop".

This is basically the one problem that needs to be solved for buses to not be rubbish, and it is so simple to do so.