Because...

All these buses, and about as many again, are waiting to get onto the roundabout behind me that I've just cycled round. They can't get on because for four-wheeled traffic it's blocked by all the cars that are no longer allowed to rat-run through residential side streets. But people won't get out of their cars and use the buses because the buses don't turn up at bus stops on time because...

An excellent example of how changing just one part of a system doesn't work.