While I do enjoy Firedragon quite a lot, I have to use Windows for work, and Firedragon alas cannot be used on Windows (not allowed to have WSL2 installed otherwise I’d use it via that). That is the main reason. If a Winblows .exe was made, I’d probably switch over, but I know it doesn’t make sense to make a Winblows .exe since it’s made for Linux. 
The only other one I am on is X, and I’m not leaving; too much fun, and good source of up to date news. 
Otherwise I agree with most of the rest of these; if I used those services I would switch (if I hadn’t already)!
[Edit] Oh and I’m already on Signal - have been for years and a Beta tester for them too