What chat protocols? Anything actually used? I tried their chat once but it didnt work with Matrix I think.
That they support Calendar is the result of CalDav I think. For some weird reason mail providers are often also CalDav providers, so you use the same account and that makes sense.
Although I would really like to have calendar and contacts as seperate apps. The combination is weird, and with some CSS it should be possible to have a single-purpose "app" with its own process ID and desktop entry with icon.
I dont know how to do that though, at least yet, as I dont know the CSS. But Libreoffice Flatpak fixed the "calc + writer shown as the same app" which is done via desktop entry stuff