Exactly this. Javascript frameworks allow overlap. I'm using the same tools and language to create a UI. Don't get me wrong I like QT apps and still tinker with them periodically. I will probably use them more once Go finds a way to make truly portable UI applications.

If only there would be a standard way of doing GUIs in HTML, but if you give the same GUI to be implemented to 10 Web developers you will get really different code, some would write it in HTML and CSS, other would maybe use angular, others would use react or similar, or if the project uses other backend language/frakework you will get different results depending on what PHP,Ruby,.NET,Java framework was used.

In Qt you use the Designer, you need to learn about the layout system if you want to do good UIs, but your GUI is saved in a file and then the c++/python code implements the event handlers and app logic.

Because VSCode is a good enough program that fits their needs and the alternative that they were using was Visual Studio? How does that say anything about native frameworks?

Because C++ is not a particularly good language to write large UI apps in.

Also, because QML is still not as good as the rest of Qt. But it's the right approach - a dedicated framework for desktop apps that is not built on things intended for completely different purposes (like HTML), but stealing the good ideas from there, like using a markup language to define the UI tree, and bindings.

Really, what we need is a cross-platform WPF with less fat. HTML is not it - it's cross-platform WPF with more fat, and not optimized for UI.

Oh, I appear to have misread your comment as "why developers move to Electron for their apps".

The reason why developers, myself included, migrate to VSCode is really simple: because it's the best all-around cross-platform IDE right now for many scenarios, and because it has a thriving extension ecosystem to tailor it further. But it is that in spite of being written in Electron, not because of it. If Microsoft announced that it is being rewritten in Qt tomorrow, I'd be ecstatic.

Just to give you an example of what kinds of issues using web tech for desktop-like experience can cause:

https://github.com/Microsoft/vscode/issues/22900

(Yes, I'm well aware that they fixed it. The point is that the offending code needed to be written in the first place. A native desktop app using 13% of the CPU to render a blinking cursor would be considered an insane bug to have in the first place.)