With federation between different Matrix servers, what’s the holdup? Why aren’t people leaving Discord?

Poor usability, confusing to get started on, your instance may just vanish at some point, annoying encryption system you have to verify new devices on, feels slow on both browser and in app, lack of features (ie; no low latency game streaming, rich presence, easily joinable voice rooms).

It also shares the same issue as Mastodon, where if your instance vanishes you can't just log in with your account on another one and have everything ready to go, because the account is tied specifically to that original instance.

Overall as a fairly techy type user I still find Matrix, Mastodon, Lemmy, etc all pretty frustrating to use.