Not a pleasant place to cycle, for all the reasons given. Also, I had an embarrassing paving slab incident there once.
But in rush hour it's probably faster than the obvious road route. And a lot of people are more scared of motor vehicles than they are of inconsiderate cyclists, blind bends, wandering pedestrians, paving slabs, bollards, etc. Hence the popularity.
500 *an hour* though. That's pretty impressive.