The only way I see to solve it is to force vendors to release hardware specs and unlock bootloaders so you can install your own software on it.

Would that actually solve it? Just because a phone has an unlocked bootloader doesn’t mean random ass people are going to want to support it. And even if some random dude on XDA makes updates for it that doesn’t mean most people are even going to want to use it. Like yeah it’s cool than a Galaxy S4 can run the latest version of Android, but that shit is buggy as hell and IDK anyone who would unironically want to use that.