Why not keep using them as...phones?
Snark aside, why are the entirely functional devices obsolete? It's because the growing demands of the endless software bloat, web bloat, feature bloat. New wireless technologies and better protocols, sure, but I've been using software for 35 years and the software contribution to this mess really gets me down.
The screen broke on my S24 but I'd still like to use the compute, ram and storage.
Because a person doesn't need to carry 3 phones, but they could be 2 security cameras and 1 phone instead?
Part of the reason why Android phones specifically are not supported for very long is because the baseband and modem firmwares from Qualcomm only receive official support and updates for about 2 years.