Earlier quoted context omitted.
Explain how QML is a mess? I've been using it almost as long as it exists - which is much longer than the life of the average hot JS framework - and didn't notice the mess. It has problems and limitations like everything, but overall it's very productive.
Essentially because require tons of fragile boilerplate code to work and it's mostly designed with web principle in mind, not desktop one. You essentially can't found a QML GUI that not exhibit tons of error, from commercial one like TeamViewer to Kde/Plasma. It's surely more flexible than classic widgets but it's flexibility is not designed in a manageable way.
Well yeah, you need to implement the properties and data models in C++ and export them - if you are doing it right that is. But the UI code is very quick and easy to write in return!
> it's mostly designed with web principle in mind, not desktop one
Not mainly desktop, true - it is designed mainly for touchscreens, mobile or embedded. It is easy to use exactly because it's not a web technology bent for user interfaces.
> exhibit tons of error
Not for the things I've been working on, which includes KDE / Plasma and many commercial applications.