They removed this support, because it was misleading users who thought they were getting E2EE when using it as an SMS client.
I’d be interested in utilization data before and after that change. Anecdotally, I use Signal much less after SMS was removed. With one app, I could opportunistically use Signal, when the other person had it, and send an SMS otherwise. Now I have to decide what kind of message to send before opening an app and learning my options. Most of those quick messages have moved back to SMS for me.