Maybe this is a US thing? I heard messaging apps are wildly different in the US. For example nobody uses iMessage here (Spain), literally nobody, not even people with iPhones. Which are admittedly very few people because they are so expensive here. Most people use budget android phones like $150 redmi's. I never get SMS either, only system/bank/2FA notifications. If someone SMSed me I would tell them to use something else because it would cost me money to reply :P

Here it's WhatsApp for 1:1 and small groups, and telegram for big public groups because WhatsApp sucks for those. I (and most of my friends!) even use WhatsApp for making calls these days. The only time I make a legacy phone call is to call a business that doesn't have WhatsApp. 95% of the calls I receive are spam harrassment so I ignore calls unless I know the number.

But Telegram is quite common for normal use to follow clubs, to follow tattoo artists, to get notifications of stock of Nvidia cards, for cybersecurity information, for our makerspace.. We really use it a shitload.

I don't use telegram for porn or piracy at all. Nor do I know anyone that does. Even though I do those things a lot, but I have much better places for it.

But perhaps in the US it's used very differently? I don't know. Here it's really quite mainstream.

It depends on the country. In Russia many people use Telegram for work and for personal communication (almost every young person has it so you cannot say it is used mainly by criminals unless you count everyone as a criminal). Telegram also has channels, so you can for example read news or (if you are young enough) funny memes there. Also, Telegram is uncensored unlike web, so you can watch videos with exploding tanks if you are into this kind of stuff. But at the same time in Japan it has a negative image of an app used for shady things.