That would mean that employers need to hire those who understand JS / HTML to build applications.

Stating that some language is better than another isn't really a good argument, most of it has to do with domain specific knowledge being leveraged to enter another market.

C#/XAML probably works much better on the desktop than Electron. Each has it's pros and cons. Also, C# is a much better language than js.

Mainly because the set of features in XAML-based frameworks is geared more towards apps and less towards documents, unlike HTML5; and probably also because some people much prefer C# over JS?

Because JS is ugly even if you put lipstick on it.