We don't need to, because AOSP works great.

linux is not secure enough to be a phone lol

if cops arrest you and its not fully turned off and encrypted with luks youre boned, and look at all the current devices supported for linux, its basically just the very expensive pine or fair phone. older pixels are fairly easy to buy in poorer countries.

then theres postmarketos which has the far larger selection of devices but most of these are quite old at this point. not to mention it uses far more resources and will drain your battery 10-20% faster