It would be nice for Apple to not do this, but if they can keep their ARM chips highly competitive it would be insanely lucrative to do so. Corporations are for-profit entities first and foremost.
If apple wanted to shut down alternative app stores macports and homebrew would already be dead.
It wouldn't be lucrative, because all the pro users (basically the mac userbase) would just not buy one. What's the point in getting one over an iPad?
Better keyboard, larger screen, more connectors. And despite a lot of devs using macs, most of the userbase aren't devs, but are instead designers, artists, or just average people like college students etc. Most of those don't need third party stores, or execute any type of software outside of an apple approved list. Give them their specialist DAW, Adobe suite, etc. and they are content.