Could be that Microsoft can navigate all the regulatory bullshit that surrounds anything government. I don't know of anyone doing that for anything Linux.
Maybe [0] will be one, eventually, but it would take a long long time to replicate the functionality if it were to ever happen. Best case scenario is that the EU were to fund an open source solution.
[0] https://www.techradar.com/pro/mozilla-launching-thundermail-...
https://arstechnica.com/information-technology/2024/04/germa...