Signal made a foolish decision to remove SMS support from their app. It was a good way to get people in to use the app and build the user base - it's easier to say to people "try signal, it also replaces your text messaging app" than to say "try this other messenger in addition to your texting app and whatsapp and etc..."

When they made the decision it was also announced on a pompous and self congratulatory way in my opinion. They posted a long post talking about being more secure rather than recognising that they were inconveniencing their users by removing a feature. Users can't decide how someone is going to send them a message but they can be advocates for adopting signal when they receive an SMS from someone.

There seems to be a lack of awareness in the Signal team of the strategic benefit of supporting SMS, when you're competing with other convenient but not as secure popular systems like WhatsApp you need a unique selling point. An all-in-one approach was a good trojan horse way of getting signals secure comms into people's lives.

While I believe in Signal I find myself defaulting to WhatsApp and my SMS messenger. Even people I know who do have signal, and who I conversed with previously are preferring to contact me via WhatsApp now. Signal is the more secure and independent option but it's convenience that really drives adoption for a lot of users.