Back in 2005-2008 or so, I think Ubuntu was a genuine breakthrough as a polished desktop version of Linux that set a standard that various other distros, eventually, caught up to. I think Cinnamon and other distros eventually caught up on polish.

They also had credible commitments to long term support that brought people on board. I think that was enough to get them on the map, but personally as a desktop user, I haven't used it in a while, mostly sticking to Debian and Arch.