This doesn’t answer your question, but I think the accepted answer is because the SCOTUS said so (with Roberts concurring).
the scotus violated the constitution by ruling that it ‘is a tax’ then later admitted that it isn’t (or vice versa- can’t remember how it went down- but the jist of the issue was that they LIED to get it rammed through, then turned around and admitted that the reason they got it through wasn’t valid-
Legal scholars all across the nation were absolutely stunned by the idiotic court opinion delivered by roberts- they could not believe the mental gymnastics he went through trying to justify his reason for voting for it- It was one of the most shameful votes ever- really- almost as bad as the supreme court inventing the ‘separation of church and state’ (No endorsement) nonsense that is now the ‘law of the land’ and the roe vs wade giving women the ‘right’ to murder innocent people fetuses