I very much doubt that is a major reason. Language itself is rarely the issue, unless you're reusing code from other parts of the project (which many projects are, e.g. VS Code with Monaco).

I have spent far too much time on HN recently in related discussions.

Having access to libraries like React and its huge ecosystem is a big plus for productivity (example vs. Qt at https://news.ycombinator.com/item?id=23154315).

Building custom UIs is also very easy with the flexibility that HTML provides (https://news.ycombinator.com/item?id=23164595), even though it can be done with other technologies (and there are some examples of that).