Yeah when I got my first smartphone and whatsapp wasn’t around yet I had to pay like 10 or 15 cents per sms. So when WhatsApp became an option everybody and their mother jumped ship and joined. For a while sending an sms and getting back I’m on WhatsApp was a thing.
Nowadays I think sms is basically part of your plan an for most plans unlimited. But they milked it way too hard back in the day. So most people just don’t use it at all.