Being centralized isn’t the only reason, but basically yes. The concept behind the protocol is simpler because your decryption keys only ever live on one device. You don’t really have the entire trust (and key sharing) model for devices that Matrix has. Signal’s desktop app works very similarly to WhatsApp where your single main device needs to be connected at least intermittently for “guest” sessions to be able to send and receive messages. I haven’t used Signal desktop though, that was just the impression I got from it. Would make sense though because WhatsApp is allegedly borrowing from Signal’s protocol quite a bit.
+1 for Lazygit. It doesn’t cover all of my needs so I have to use the CLI for a few small things, but for 99% of your typical git usage this tool is such a gift.