Maybe you are too young, but there was a time were we used RADs (Rapid Application Development) environments like Delphi, VisualBasic, Visual C++, etc. Those solutions which are from 1990s, are still years ahead in simplicity vs what you need to do to build a full web solution today (front-end and backend). Of course the web has many other benefits, like 0 install, runs everywhere, always updated, etc., but calling web development simple is just crazy in my humble opinion.

What are the incredible benefits of the web? Have you worked on a complex QT app?

I have worked with both, including Widgets and Quick. I wonder why you think Qtcom is focusing development on Quick, which uses QML (JSON-like syntax) and JavaScript (ES6), while declaring Widgets "feature complete", mostly releasing minor fixes, in other words, keeping it stagnated. The obvious answer for me without getting into Mobile vs Desktop development is: it's easier to get new professionals to use technology as popular as JS (or any other web related stuff), and definitely cheaper for companies to hire said professionals, therefore making it a easier pick for new projects. To summarize the benefits: easier for junior devs to use and because of that overall cheaper/faster deliveries. Note that I'm not saying anything about quality.

Junior developer doesn't mean a developer who just knows JavaScript. Cheaper developers doesn't mean faster or cheaper delivery in the long run. And I don't think brundolf meant cheaper developers.

I have seen a LOT of Qt apps and 100% of them had worse UI than your average web app.

I've seen lots of Qt apps. Most of them have been much better than the average web app.