The only large group of people who still primarily use SMS to communicate person-to-person is Android users in the USA.
Every other country has settled on either Telegram, WeChat, WhatsApp or FB Messenger, or other niche apps. These apps work on both iOS and Android and often also Windows. I haven't sent an SMS in probably 12 years. I don't know anyone who has.
It's only in the US that iMessage is so prevalent that Android users have to use SMS, the only other way of messaging iOS devices. And the US is quickly becoming a de-facto iOS only country. It already has more than 50% market share, even 80% among young people.
With the US going (almost) full iMessage and the rest of the world having already settled on another app there simply no point to supporting SMS.
Typically, if I try to reach someone but they don't answer I'll follow up with an SMS to explain what I tried to call for. If it's a co-worker, or an acquaintance, I'll send an SMS to make sure they receive my message. SMS is more reliable, doesn't require you to know which apps the other party runs, and it comes through to the recipient as SMS is a basic service in the telecom networks.
When I get to know a new person there's a transition to "oh, you're on $APP too", and I might starting moving non-urgent messages to $APP. But if you don't know the other party well or there's a question of reliability, what is an alternative backbone for messaging if not SMS?
Here in the UK, whatsapp is the default first try, at least with anyone I've interacted with. The dog groomer even messaged me on whatsapp to tell me dog is ready, completely unprompted.