I understand why (tying to avoid the "yet another Linux distro" stigma), but when you go to "What is Qubes OS?" in https://www.qubes-os.org/intro/ ; they fail to mention that is Linux based.
Well, to be fair this one has a FAQ entry: https://www.qubes-os.org/doc/user-faq/#is-qubes-just-another... ; although they try to understate that they use Linux.
If they want me to trust them, they're doing it wrong.