If the brands were any more competent at servicing watches, I would probably be more inclined to agree with the basis of your thoughts here, but there is ample evidence they are not.
Rolex does a decent job, but not without issues for sure. The others are not all that good at all. Some of the hack work I have repaired has come from the brand service centers here people have sent the watch to me to fix the problems the brand created after several attempts to get the brand to do it right.
So you have basically summarized the reasoning these brands give for cutting off parts. So the question is, has this solved the problem of hack work being done on watches, or has it made the situation worse? Do you think the hacks will stop hacking just because they can't get genuine parts?
People throw around various ideas of how watches will be serviced in the future, including things like 3D printing and generic parts. I have seen generic parts that were virtually indistinguishable from the originals, and I have seen generic parts that in no way would I put inside a watch movement I was working on. Which ones do you think the hacks are going to choose? The cheap crappy parts, or the good quality and expensive parts? The guy I described above apparently used to work for VC, so has pretty decent watchmaking credentials...
There is no simple answer here.
Cheers, Al