Cheaper devs.
Yeah, no, it's not "cheaper devs". This is elitist gatekeeping.
HTML/CSS/JS win because at this point there's both a mountain of features that you'd need to match in a native framework, it's cross-platform with rendering engine(s) that are mostly platform agnostic, and it's _actually documented_ unlike things like AppKit.
Someone learning HTML/CSS/JS can google their issue and find a solution or guide or what-have-you with relative ease. It's nowhere the near the same for any other framework.
HTML/CSS win for a reason. ;P