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.
> I don't get it how having a dozen of messaging apps and remembering who uses what is better than a simple SMS
Indeed, especially now that Telegram is taking off by times in Europe (in Belgium / Spain / France at least Telegram is getting used by a lot of people) and that some people now refuse to use WhatsApp.
In addition to appointment reminders from doctor/dentist/notary/whatever and delivery tracking numbers I still exchange SMS with quite some people.
It's not as if it was exactly hard to open and reply to a SMS you just received from someone: takes exactly the same time as answering using WhatsApp or Telegram.
Interesting, here in Germany, almost everyone I know has Signal and WhatsApp with some people using only one of them. Telegram I encountered from one US American living here, and from people into conspiracy theories.
As for Telegram, people mostly use it to consume news. It basically replaced RSS readers for common people. Although its install base is relatively high, I have yet to receive a single private message over Telegram.