My guess is just a QA burden: they probably test the firmware cleaner utility on those operating systems, and they don't have the resources to test and certify the firmware tool on every conceivable distro.

Maybe it will run fine on Fedora, but if it bricks your laptop, they don't want to get blamed.

I'm not sure their motives for this choice, as their means of disabling as much of ME as possible is ME cleaner, which is not tied to distros.

I don't see why you can't attempt to do it manually yourself, without the aid of their driver and firmware update tool. Except that you might forfeit any warranties/support.

System76, can you clarify?

Sadly it's standard to only see official support for Ubuntu or RHEL in the Linux world. Not that I don't understand, it's all very fragmented, and that creates a lot of work as to support multiple distros. People are working on remedies, though.