> over Debian/Ubuntu
And over Fedora/RHEL. If I had to guess, it could be that new entrants find it easier to submit changes to Arch Linux packages [1]. ChromeOS also steered away from Debian-based distributions, choosing a Gentoo base.
[1] https://gitlab.archlinux.org/archlinux/packaging/packages
[dead]
They're not though. They're supporting debian and bazzite which is fedora based and have worked with fedora extensively. See https://frame.work/de/en/blog/framework-sponsorships