Social graph? Americans tend to know other Americans, Europeans other Europeans, on account of geographic and political proximity. Possibly the divide is a symptom of the underlying communication network.

I think it was more about companies than individuals. European companies (e.g. SUSE, Mandrake) defaulted to KDE, whilst US companies (e.g. Red Hat, Novell) to GNOME.

I don't know why. Maybe it was RMS who pushed for GNOME as back then Qt wasn't free software (as in FSF or OSI approved license). Maybe it was that KDE started in Europe and later GNOME in the US to provide an alternative to the “non-free” KDE.

This caused European funding (from companies and institutions) to go to KDE, and US funding to go to GNOME, thus creating the communities and ecosystems we have today.

Another point for GNOME back in the day for companies, was that it was (could be?) more locked than KDE and it had less customization options. These are desirable traits if you want to install it to your company's workstations, so maybe it made sense for Red Hat to adopt GNOME.

The key point in time where GNOME became way more popular, was when Ubuntu came out with GNOME as the default desktop. A smaller point was when Novell bought SUSE, so SUSE switched to GNOME, leaving almost no commercial distros that default to KDE.

All in all, it doesn't matter much anymore. Our life and workloads have moved to the cloud and locked down devices, thus limiting the surface area of desktop environments and their ecosystem.

Do they? Ubuntu, Mint are both European are using Gnome or at least GTK.

Red Hat/Fedora uses Gnome because Gnome is basically a Red Hat product. This has nothing to do with the geography of the distro.

Unfortunately, a lot more people use Gnome. Which is a shame in my opinion. But it is the way it is.

How is Ubuntu European?

Mint I'll grant, though I always thought of it as a thin fork of Ubuntu. Interestingly the first version was based on Kubuntu - I wonder what motivated them to change, but the old release notes appear to have disappeared.

Canonical is a UK company.

It is undeniable that corporate Linux has prefered GNOME over Plasma, I can't name you a single relevant European distro that uses Plasma as its default.

- Canonical (United Kingdom) ships GNOME for Ubuntu.

- SUSE (Germany) ships GNOME as default on their SUSE Enterprise Linux, openSUSE hsa no defaults.

- Manjaro (Austria, France, Germany according to DistroWatch) ships XFCE (GTK based) by default.

- Mint (Ireland) ships 3 GTK desktops, defaulting to Cinnamon.

Meanwhile, on America:

- Valve (USA) ships Plasma on SteamOS for their desktop experience.

- System76 (USA) ships (although they hate it) GNOME for PopOS. They want to replace it with a Rust-based, GTK/Qt-free alternative.

- Red Hat (USA) ships GNOME as their official desktop for RHEL.

- Fedora (USA) ships GNOME as their official desktop.

So I don't think country impacts much, it is just that GTK is the de facto toolkit for Linux and historically, Qt wasn't FOSS and GNOME received a lot of development for accessibility during Sun's days, which matters a lot for corporate due to stricter requirements on that front.