I still compile a old project in Delphi 7 once every 3 months just to add 5 lines of code, and they pay me monthly for it. It's cheaper than porting the whole system to any other language. It is a project that I've built 8 years ago. Delphi was already a "strange think" on that time, it was declining fast. I think Java killed Delphi - "One codebase for all platforms, even your freezer will have Java!" - this was the…
"But I still miss the old days of drag-N-drop GUI of Delphi, really easy." How many years later and the web still does not catch up.
1) JS isn't discoverable from the perspective of the IDE. There's no static typing and no way for the IDE to hook up code to UI elements, and vice-versa. You need a statically-typed language that can transpile to JS without too much "impedance mismatch".
2) HTML layout functionality isn't really geared for the type of layouts that are present in desktop applications. Document-oriented layouts have a completely different set of requirements.
3) You have to solve the design-time/run-time issue, and this is not an easy issue to solve due to 1). You can't just use a browser engine at design-time for the WYSIWYG portion, so you need to create a whole "browser emulation" layer in the IDE, along with an execution environment for your statically-typed language.
Our product, Elevate Web Builder, solves these issues and implements a Delphi-like IDE for developing single-page web applications:
https://www.elevatesoft.com/products?category=ewb&type=web
We've got a new version coming out soon that will also offer server-side coding in Object Pascal, giving developers a single-source-language approach to developing complex web applications.