The part that takes time in UI isn’t wiring up components, it’s the small changes like something is a pixel to the right or that gap is two pixels wide. Changing those in a C++ project means recompiling and that adds up to significant overhead over a day of polishing the UI. If C++ was able to get builds out in less than a second, this wouldn’t be an issue. People value performance in their own tools more than the tools of their customer.
In modern Qt you don't write UI in C++ anymore - you do that in QML. It is far simpler to create amazing pixel perfect UIs with drooling-inducing animations in QML. I wrote a blog post that talks a bit about this[1].
[1] https://rubymamistvalove.com/block-editor
In wxWidgets you use sizers, so you don't work on pixel-level alignments. I can understand if you're using an ancient framework like MFC, but even then I seem to recall there was a sizer equivalent system (or it is easy enough to write a class to do so, moving components).
I think it is a daft thing to move to shipping a colossal web framework and entire browser simply because of 1px UI alignments (which have been a solved problem for decades in C++ anyway).