I believe that ubuntu mate is a branch of ubuntu. So why cant people get ubuntu desktop on raspberry pi?
It’s mostly due to the hardware limits and experimental software support for the graphics stack that Ubuntu desktop (Unity or GNOME 3) requires. The Raspberry Pi has 512 MB or 1 GB of RAM depending on the model but Ubuntu recommends 2 GB.
Ubuntu MATE is a flavour of Ubuntu, but the images so far are based on a side project called Ubuntu Pi Flavour Maker. The project mentions other distributions including Ubuntu, so it is possible to build, apparently:
What Ubuntu Flavours are currently supported?
The following Ubuntu flavours can be built by the Flavour Maker and work in an almost identical manner to their PC counterparts.
The following Ubuntu flavours can be built by the Flavour Maker and work with varying degress of success, this is due to the experimental nature VC4 OpenGL driver these desktops require:
Ubuntu (GNOME 3) should be able to run on the Pi 3 with the experimental OpenGL driver but since GNOME is such a resource hog, you wouldn’t be able to do much with it.
I’m working on porting a whole bunch of Ubuntu 18.04 flavours to the Pi 3, but GNOME won’t be included.
2GB is the absolute minimum for GNOME 3 if you don’t plan on running any programs. You can get away with GNOME on 4GB RAM but don’t open too many programs or browser tabs! 8GB RAM is good for GNOME since GNOME itself takes up about 2GB!
What is the reason GNOME 3 takes up so much RAM because if the PI can handle the GNOME 2 task bar well then cant there be a type of GNOME 3 that uses less RAM by having different menu or something.
I’m sure GNOME 3 has a ‘fallback mode’ which makes it look more like GNOME 2.