Why don't folks just use Matrix protocol?
In contrast, Zulip is fast, simple, and “just works”.
I've been running Element flawlessly for two years now, including a Synapse server. Never had it more "just works" before.
Personally I use Element every day to keep in touch with the Matrix community, and it works fine for my minimal needs. It’s better now than it was then.
Hint: It's not a fun experience.