Many many Linux users are all for nice UIs, and pretty animations. Which is why GNOME, KDE, XFCE, MATE, Cinnamon, Budgie, Pantheon exist in the first place.

The sheer amount, variety and quality of themes available for a typical Linux distro puts your point to rest.

What puts my point to rest is that the only successful Linux based consumer devices, are a web browser based OS and a Java based one, with nothing Linux specific exposed to its users or app developers.

So how does DCO differ here? I'm not getting anything from three words.

The DCO is not a CLA. It's more a document that says that the submitter is indeed the copyright holder of the submitted work (or his/her employer/etc. is) and that the contribution is licensed under the same license as the original software.

See https://elinux.org/Developer_Certificate_Of_Origin

Facebook is like Oracle of my generation. As their products fades out of mainstream, they just buy next big thing and keep the ball rolling.