(a) Not everyone has a (smart) phone.
(b) Not everyone can use a (smart) phone.
(c) Not everyone wants a phone.
(d) Not everyone can afford a phone.
(e) Not everyone wants to upgrade their phone to use the newest shiny things.
(f) Not everyone can upgrade their phone (see (d)).
(g) Not everyone opts to put (third-party) apps on their smart phone.
(h) Not all apps are built with accessibility in mind (see (b)).
(i) Some folks are concerned about mass surveillance (see (g)).
(j) Sometimes phones get stolen.
(k) Sometimes phones get broken.
(l) Sometimes phones get bricked.
(m) Sometimes phones get hacked.
(n) Sometimes phone get locked out.
(o) Sometimes apps stop working.
(p) Sometimes cell service goes offline (see Hurricane Helene).