The backends are also not documented, you need to try out what's working and what isn't working. It doesn't explain the supported and unsupported features of each backend, neither their quirks.
A lot of behavior is surprising. For example if you have powershell in path on windows inside MXC it will just silently add the whole C drive with read-only permissions. Circumventing all other policies. https://github.com/microsoft/mxc/issues/1455
A lot of common error cases regularly happen and don't provide reasonable error messages. No documentation how to deal with them.
Check the issues on GitHub, there are many things that are expected to just work and they don't. One would at least expect some documentation why it doesn't work and where the limitations are: https://github.com/microsoft/mxc/issues
This actually confirms my guess: https://news.ycombinator.com/item?id=50018898
But if it doesn't deliver...?
And maybe no other tools tried to do this because it's not a good idea in the first place (and I have plenty to say about that)?