They were only interested in the platform inasmuch as it could give them a way out of the hole they had dug for themselves with Symbian. They threw out half-assed implementations of this and that and then abandoned them at the speed of light, because the only real focus was migrating their historical Symbian devs to something that could resemble XXI century tech. I know because I was mulling some projects in the space at the time - I even went to a usergroup event that was supposed to be about Qt and got sold what was clearly a "Qt for Symbian" slide deck.

Trolltech was skimpier but was much more interested in the success of the platform per-se. In many ways the post-Nokia experiences are an attempt at re-discovering the space Trolltech lived into.

> their open source OS based on Qt.

There was never such a thing. They had a Symbian OS skinned with Qt, and a number of Linux incarnations that started with GTK and were later reskinned with Qt. It didn't help that they stroke a high-level agreement to basically adopt Intel's Linux efforts, which were targeting GTK. By the end of these travails, they ended up with something fairly decent but that was just a lame-duck. Nothing was ever "based on Qt" at a fundamental level.