Why would you expect that doing something that goes against what everyone else wants, would have been made easy for you? You're basically becoming your own "distro" of Windows. Of course that's hard.

But the point the GP is making is that it's also not totally implausible to do, if there were any real motivation for people to pursue it.

There was a real reason for people to want to "take control" of Android, and so we got LineageOS.