In multiple European cities now I see taxis being allowed to use the bus lane (while of course regular cars are not).

What's the policy justification for this?

I like it. 

When I need to move fast to e.g., catch a plane, I take a taxi. 

Taxi drivers need to have a license, so they pay back some money to the city for utilizing the bus lane.

Building @kiwi 
Writing @ https://kanfa.macbudkowski.com/

If the goal is to charge for priority access to give a way for people who really need it to get priority and raise revenue, why not decouple the "taxi vs car" aspect from the "paying for priority or not" aspect?

I know plenty of rich people who don't even have their own cars, and uber everywhere.

(I'm one of them, but as a nomad having my own car is impractical; I mean more stationary types)

The parking thing is legit, but could be addressed by parking fees?

IMO because:
- rich people would just buy this access and use the lanes even when they're not in a rush,
- taxis are shared and utilized most of the time vs. private cars that move from point A to point B and get parked.