Maybe you use low end phones or crappy vendors?

I'm migrating from my 5 year old flagship (lol) only because vendor decided to stop supporting it. Battery still good for a day, great screen, good enough camera, fantastic sound, ssd card slot...

My next has at least 7 years of mainline support (with all AOSP releases) plus at least couple of years damage control updates.

It's a matter of the choose I think.