Take this with a pinch of salt- I seem to recall that last time this subject came up it was explained by reason of the bus lane being too narrow for a bus to pass a cyclist.
Which never sounded very convincing, I will admit.
There are government guidelines about how wide a bus lane should be and how wide it should be if bikes are allowed.
There are government guidelines about how wide a bus lane should be and how wide it should be if bikes are allowed.
But iirc most local government ignores it.