Qt is actually not that good. I used to work for a large, well-known software company that distributed an app using Qt; every day that I worked on the native client was a nightmare of framework bugs, quirks, and limitations. For all of CSS' quirks and limitations, it's still an order of magnitude less frustrating to develop with a TypeScript/React/HTML/CSS stack than it is to use Qt. TypeScript is also a vastly better language in most respects than C++ or Python, the only two blessed Qt languages.
I don't know what "[it] was not as productive as it was" means (it's a logically nonsensical statement, so I assume you made a typo). It was not an especially great (though not terrible) or productive place to work, I'll give you that.
For colour, I'll add: it was a fairly old application first developed before QML/Qt Quick. It was also a multiplatform desktop application; then and now it's unclear to me as to whether or not Qt Quick is especially suitable for desktop applications.
We'd been in the process of moving chunks of it into an HTML/JS web view for several years - I think when that decision was first made it was well before QtQuick would've been sufficient for desktop usage. Other reasons we were doing it, besides the aforementioned bugs/quirks/limitations were that it's easier (and cheaper) to hire web devs than native devs, and that it allowed for code/infrastructure/design reuse with our web frontend. QML doesn't address either of those issues.
Admittedly, I haven't tried QML in anger, but I also feel like...given the quality of the rest of the framework, which is comparatively mature, it'd be pretty shocking to me if it didn't have its own slew of bugs/quirks/limitations.
