Well personally, I like to have organized chat rooms or "channels". Matrix is closer to a user friendly IRC client. Signal is great for group chats but some people are looking to have organized chat rooms for their friends.

Someone will eventually ask "why not just use IRC?" and the answer is simply: Would your non-tech-inclined friends enjoy doing that?

I love Signal, but it's not "IRC-shaped" like Discord, Slack, Matrix, etc are. It isn't built to play the same role.

Because Signal has a single point of failure and actively fights with decentralization?