A difference between Discord and Matrix(/IRC since it was brought up in the comment as well) is that there isn't a single client because they are open protocols.
If a person doesn't see a usability problem, it might simply be because they are using the right client for them.
Always remember that nothing is free, and FOSS is no exception; you might have to invest some time and efforts to make it work for you.
Matrix has a flagship client that you can find endless usability complaints about.
I myself downloaded the new Element X app on my phone to evaluate it a bit just now, and it doesn't even have a way to sign up during the onboarding process. Do you realize how much of a failure that is in terms of UX design? When the average user won't even be able to get past the sign in screen?
Element X is not finished or intended for average users yet, as https://element.io/labs/element-x makes clear. Itβs a preview of the future of Element.
If a person doesn't see a usability problem, it might simply be because they are using the right client for them.
Always remember that nothing is free, and FOSS is no exception; you might have to invest some time and efforts to make it work for you.