Good luck trying to convince the general population that “the UX is bad but theoretically anyone can improve it” is better than what you get out of the box with other messengers.
Just do the change yourself. Help those people close to you to install Element alongside whatever they are using now. Even if just because they are using to talk with you, it's better than nothing.
You don't get to migrate things that are on huge network effects in one go. But we can help the growth of one network organically until it reaches critical mass.