Are we really comparing RAM here as if it were the 90's? How many people here use Android? Today it needs 512 MB to function properly. In two years that could be 1 or 2 GB and that's a mobile OS. How much RAM does your browser use? My Chrome/Firefox easily uses 1 GB. My GNOME 3.10 desktop (running Fedora now because I needed a modern GNOME version for Exchange support for work) is using about 800 MB to 1200 MB. Do I really care? No, because RAM is cheap and I have 8 GB. Do I need to buy more? No, because 8 GB is still more than enough.
If you can't run GNOME because you don't have the system specs to run a modern desktop then you can select XFCE/LXDE in the installation menu. But let's be fair, those people are a minority. And a default should fit the needs of the majority. And since people easily have 4 GB of RAM or more these days with the basic 3D acceleration (even a Raspberry Pi can run GNOME 3) then I would say that logic chooses GNOME. Also because of a ton of other reasons already mentioned e.g. systemd, documentation, dedicated maintainers, accessibility, etc.