To make non-App-store apps annoyingly unusable, so the App store will sell more apps, instead of people downloading in other ways?
Just like Apple cripples the Safari browser and PWA apps.
Long term, maybe Apple wants to be able to remote-forbid apps if Apple is developing their own competing app?
Whilst most developers working at Apple understands this, and don't like it? Maybe the developers even feel happy about people here at HN being disappointed, and think that "now the business people here at Apple notice that this causes disappointment" ?
If this drives developers from OSX to other OSes, chances are they will develop apps for those OSes first.
Apple is too big to fail at this point, but driving developers away from your platform isn't a very clever strategy. You never know when you are going to hit a tipping point, and after you notice and people stop using macosx for development its already too late.
It took me ~150 hours to migrate to Linux, but my user and developer experience on Linux is much better than on MacOSX (emacs daemon "just works"!!!), so after all that work I wouldn't consider switching to OSX in the next 5 years at least. I had a Macbook air 2012, and because Apple still hasn't released a laptop that isn't a downgrade from that in some sense (keyboard, magsafe, ...) I've went with a think pad instead. Tiny details, like having a webcam that doesn't suck now prevent me from going back to OSX.