So many apps even refuse to be installed on older versions of iOS/Android.

That's because they see older versions of Android decrease in usage so they think it's fine to lock them out and potentially lose customers[1], but they're not going to do that to the majority of them.

If the majority stops falling for the propaganda and "upgrading" to a worse experience, other businesses will follow.

[1] I have told businesses that changes to their site have made me no longer want to do business with them, and seen responses ranging from complete dismissal to quick reversion.

Yet another reason to dump iOS/Android : planned obsolescence of this form.