Signal is a centralized app, run by a company. If they are offered enough money or legal threat they will sell out or close.
I am sure people will make an argument that its FOSS and people will just fork it if it goes bad, but a new fork will have 0 users and Signal will still have all of your old contacts. Why not make a switch now? Before it is even more popular and you have more reasons to stay? Why fork it if there are already decentralized apps that use same encryption, like XMPP apps?
Sure you can find flaws in every app, including XMPP implementations, but if we will have to write code for a new Signal fork, why not just fix whatever is that bugs you in XMPP clients?
If you want to use Matrix, that is fine as well, we can always bridge the two open protocols. But you cant bridge Signal if their company doesn’t allow it.
Why would you trust Signal more than XMPP that uses same encryption? I think people are just afraid of things they haven’t heard of, even if they have been there for longer and have a better reputation. This is why marketing is the biggest business in the world, google and facebooks only revenue is selling ad space and they are richest companies in the world. Fight that marketing, learn a bit about XMPP and you will see it is far better than Signal.