UIs don't need to look the same, and there's no reason they should. Choice is a good thing. The problem, however, is a lack of interoperability: Gtk apps look like shit in KDE and vice-versa. There's no good reason for this; it's possible to make it so apps with different toolkits blend in seamlessly, but the Gnome devs are infamous for being completely unhelpful here and having a "our way or the highway" approach to everything.

>Because while you think gnome3 sucks if Canonical had their way everyone would be using it.

Not true; if Canonical had their way, everyone would be using Unity. Honestly, I don't begrudge them making Unity; it's good to have some diversity, but I do begrudge them switching to Gnome3 recently and abandoning Unity altogether. A lot of people liked Unity and its concepts. Instead of throwing in the towel and becoming yet another me-too Gnome3 distro, they could have adopted KDE, and then created a custom KDE theme or version of Plasma which looks and works like Unity and allows them to continue to explore those concepts which leveraging the existing KDE underpinnings and the superior Qt toolkit. The real problem IMO is the horrible Gtk toolkit: it's in C but bolts on a hacky OOP concept, it's undocumented, and it's constantly changing. I know of at least one commercial project which had to abandon it and switch to Qt because of the constant API deprecation, and there's at least one FOSS DE (Lxde I think) which also switched from Gtk to Qt for the same reasons, and got a performance boost in the process IIRC.

>the alternative is to stagnate with accepting what we have.

I can't even count the number of comments I've read from people who are sick and tired of the constant change and churn in Linux UIs. Lots of people were perfectly happy with Gnome2, but then it was deprecated and they were pushed to Gnome3 and it was terrible and they hated it. As a result, not 1 but 2 new DEs were created, just to satisfy people who wanted something more stable: Cinnamon and MATE. It's a complete mess. A lot of people were similarly pissed when KDE4.0 was released and they couldn't use KDE3 any more because the distros all deprecated it, and the new version was filled with huge bugs and didn't work. At some point, you need to aim for product maturity instead of constant churn. I've been using ssh for many, many years and I don't see that being deprecated any time soon and having to switch to some other standard, but somehow we're supposed to accept this as normal for DEs?