You assume everybody wants to spend many hundreds of dollars on a cell phone.  I don't.  I make phone calls and send texts; that's it.  So for me, an older (even used) phone is fine.  The problem is, VoLTE is a requirement, and though many phones say they are LTE compatible, they may not be VoLTE; they aren't the same thing.  Commonly available information doesn't make that clear.  This is the flaw in "Bring your own phone".

To make matters worse, you still have people selling phones that claim to be Verizon compatible; they are . . . until January 1, 2020 at which point they become paperweights on the Verizon network.