How come the minuscule userbase of native frameworks have better tooling than the numero uno popular web? It may mean that there is a technical reason in the background.

They solve a simpler and more constrained problem which makes it easier to make tools. Something like Windows Forms are basically WYSIWYG - you drop some controls on a canvas and now you have a GUI. But the GUI will not gracefully adapt to different screen dimension from large monitors to mobile.

Native frameworks support flexible and resolution dependent layouts too.

Responsive layouting is an orthogonal problem.

Orthogonal to what?

30+ years of history?

Interestingly enough JavaFX is much younger than the web, and is quite niche, yet it has SceneBuilder.

It's younger than the web but much older than the current bunch of frontend technologies. JavaFx is from 2008 [1]

Anyway, that's not very important.

What web apps never had is a visual app builder as popular as the first Visual Basic for Windows 3. We had some tools like that (example Jwt [2]) but none of them got a critical mass of users. Maybe it's difficult to match Visual Basic's success because Microsoft controlled the tool, the operating system and the language. If this is the case the only current candidate is Google, because of Chrome. They are investing on Flutter and Dart now but making them prosper on the web looks like a uphill battle. Much easier on Android.

[1] https://en.wikipedia.org/wiki/JavaFX

[2] https://en.wikipedia.org/wiki/JWt_(Java_web_toolkit)