Skipping discussion about "actual security": vendor lock-in & network effects. None of my peers uses Signal for everyday communication. Quite a few use Telegram, +Telegram channels & conferences, bots, and, well, honestly, it's really quite nice app to use. So, yeah. It's sad.
True. Then again, Telegram really has no encryption at all, since no one uses the secret chats. So he probably meant something like "why not use an app that actually tries to do what it claims to?".
That's why I chose to skip discussion about "actual security" in favor of answering the actual question somebody asked. I agree with your point completely.