And regarding fragmentation, GTK+ vs. Qt has never been the main issue. It's been different distributions and the fact that app creators cannot ship apps easily to all distro's themselves.
But, I believe, the main issue behind Linux Desktop has always been lack of corporate interest. There was some in early 2000's but never anything serious.
Windows and Mac "are" ecosystems due to financial motivations.
Fragmentation is one of the double-edged swords of all open-source projects. It leads to greater innovation, at the expense of duplication and wasted efforts.
I would still rather have the freedom to choose and contribute to a fragmented ecosystem, rather than have to be forced to deal with issues in a black-box propitiatory OS with "unclear" motivations...
I blame the KDE vs Gnome fragmentation, and over-customisation.