That's like saying Tulip blocked the installation of Vista because they didn't install enough RAM to run it

The OS makers don't have to go out of their way to support a device they don't want to (that's the beauty of open source passion projects), but it's also not like any manufacturer (that allows bootloader unlocking or ships an unlocked bootloader) is blocking GrapheneOS or anyone else from doing it, which the quote implies in my reading (maybe other people read it differently)

This is a contradiction. There is nothing "minimal" about a requirement that excludes every device but one. Also some people (me) value independence from Google more than the highest degree of security (which relies on Google hardware).