We need an alternative to QML, something that's honest-to-god compiled and not interpreted. And fast.
We need our desktops and phones to be responsive and our software to work on any old thing we manage to find.
QML may not be fit for our purposes. As we are mostly using x86_64 desktops it's very easy to get used to responsiveness.
But if we want our software to really work in ARM world we may need to reconsider our choice.
* QML code is easy to write but it takes several rounds of profiling and review to free the code of resource hogs
* QML is quick due to caching and JIT but this brings complications and debugging difficulties when you encounter a bug
* QML is JIT-based, which means slowness in first use of plasmoids and apps and increased memory usage after code is compiled