No one is going to use Matrix that doesn't have privacy-focused contact forcing them to because the privacy benefit of the slight inconvenience is something almost nobody cares about. Things that are non-issues to someone who read the online Matrix documentation becomes a mountain to a middle aged mom who taps through errors without reading them and is used to things "just working" in the way Apple products just work, not the way Linux just works.

If you log into multiple devices, you have to go through a verification process to verify the new device. You may need to backup and restore your encryption keys manually or all your messages will be "Unable to decrypt message". Keeping multiple clients open simultaneously is supposed to have one client request the keys from the other client, but this either takes a while or doesn't always work. I have a contact with an unverified device (so all his messages show up with a warning) who refuses to fix it because all the other messengers just work by logging in. This is on top of people being upset that you're adding one more app to their menagerie of texts, Facebook, Whatsapp, Telegram, Discord, etc.

I use Matrix with my close contacts but I can't imagine anyone ever saying "Damn, I'm going to use this instead of Discord now!"