Let me see if I can explain this better …
So, beginners learn that rotate in perspective works great, but when they accidentally do the same command in any 2D viewport, its gets warped. If they spot the option “Only pan parallel view,” they think its fixed. It’s not. In their minds, you should not be allowed to ‘break the interface.’
Remember, people are learning and have no frame of reference. They are doing the wrong thing ALL the time – and not even realizing it. Sometimes, students won’t notice their ortho view is a few degrees off. I’ve seen them do work for a while … and then its all distorted … and they have to throw away work and start all over. I usually spot the problem before they do!
I totally get that this does not make sense to an expert like yourself. Me neither. But, I have to adjust to my students and this is a long-running and constant source of confusion.
You are right that there is a use for rotating an ortho view. I am not sugesting doing away with it. It should just be a lot harder to do accidentally. I suggest an option listed under the viewport label ‘rotate ortho view’ or ‘unlock view rotation.’
I hope that helps.