• 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.