Custom roms can be just like distros. The problem is non unlockable bootloaders and device attestation and that's only getting worse with the help of the govs. If we wanna try something, it would be directed here. But they're really convinced only big corps can do it.
Anything else installed on a device, including GrapheneOS, will render it a dumb device. People don't want that, they don't even want freedom actually. They don't want linux, never picked it up for decades. It'll even get banned.