I've never understood why they are. They are not public service vehicles, as buses are, they are private businesses. They are not reducing congestion, as a bus is, as they quite often only have one passenger who might presumably otherwise have taken the bus.
I ride a bike and get sick of taxis harrassing me in bus lanes. As a driver I also get sick of taxis speeding past on my inside then cutting in at the last minute to get in the 'normal' lane.
AIBU?