They use SMS because it's a baseline that every phone, smart or dumb, has. No need to have an email address, no need to have an app.
Most people use Whatsapp / Messenger / social media / to a lesser extent iMessage.
My phone is an IP phone. It doesn't do SMS. Did you mean "mobile phone"?
> No need to have an email address
I'm pretty sure that more people have an email address but no SMS capability, than have SMS but no email capability.
UK landlines are transitioning to VoIP. SMS messages sent to UK landlines are read out by a text-to-speech system (well, my parents' does).
They use SMS because it's a baseline that every phone, smart or dumb, has. No need to have an email address, no need to have an app.
Most people use Whatsapp / Messenger / social media / to a lesser extent iMessage.