In my opinion, relying on upgrading users automagically to an encrypted and secure protocol isn’t good practice. If someone wants to use an encrypted chat, they should do so consciously. It will only cause confusion otherwise.

This is my theory for why they ditched this feature - the ultra-concerned about privacy superusers don’t approve of its messiness, even though in practice it’s the main engine for user growth.

Do people still use SMS these days though anyway?

I would have thought iMessage, RCS and separate chat apps like Whatsapp, Signal and WeChat would have largely replaced SMS by now.

SMS, MMS, iMessage and RCS are all compatible with each other and mostly used interchangeably and are the main way people text each other (in the US anyway). You just have a phone number, and when people text it with any of those formats you receive the message and respond the same way.