- Unlock bootloader (depending on vendor, you have to do an online verification),
- flash a recovery.img,
- load into recovery mode (which, depending on the phone, might need extra work)
- wipe some caches,
- select new os/rom image,
- pray it doesn’t brick your phone.
You’d think someone would’ve learned a thing or two from the easy graphical installations linux and even windows have been offering since the late 2000s.
In summary, the corporate bean counters don’t want to give up control over your device. That’s really all it boils down to. They’re not doing anyone any favors, that’s for sure. It’s pure greed