Tax data is government data. Government data is public data. Instead of asking "what's the reason for making something public" the question is "what's the reason for making a carveout for some specific data to make it secret"
Government data about private individuals can be considered as private, for privacy reasons. If the government knows that I have a mental disability, should everyone know about it, so they can discriminate me accordingly? What kind of dystopian view of the world is this?
Or, if I own crypto, why should the government facilitate the work for criminals?
The Government IS the public. I agree that the public shouldn't necessarily know about your mental disabilities, but then you just shouldn't give this information to the government.
Giving this information to the government is needed to get either financial help, or just a card to justify accommodations. But yeah, let's create second class citizens out of disabled people, great idea, very "scandinavian" indeed. At least they stopped sterilizing them.
The Government is answerable to the public and should serve the public. But conflating the government with the public is simply bizarre, to my way of thinking.
Governments should be transparent as much as possible, yes. But that doesn't mean being necessarily transparent with sensitive information that they know about members of the public. Only with your (bizarre to me) conflation of the public with the government would this make any sense.
Or, if I own crypto, why should the government facilitate the work for criminals?