This is because on the web, everything you see on the page has to be downloaded first. This leads to the following cycle:

* a widget toolkit is created and gains some traction.

* It starts adding features, becomes bigger and slower to download and execute

* users start leaving for the next toolkit, which promises a smaller, faster experience.

At this point, most webdevs have simply given up on desktop like toolkits, and only use what’s available on the browser, combined with a few lightweight libraries and an ui framework