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?

a doc and general practitioner by day, a geopolitics junkie and deep onchain comms shitcaster by night and both in /doctorsphere

But for the purposes of congestion management, taxis *are* personal vehicles?

The idea is to have less parking lots, ideally, leaving now space for "walkers". Personal vehicles in true sense are used for a fraction of the day, so if you make it more convenient to reach your destination by other means- you would normally do so.
Increasing parking tolls serves the same purpose.

Yes, but what is better for environment and traffic when one car delivers 30 peoples or 30 cars delivers 30 peoples?