I'm very into the idea of HTML/CSS/JS on the desktop (and by extension, things like react native), even if simply as a frontend to a heavier duty application running on localhost. I feel like the OSs should be shipping runtimes for it instead of having insane 120MB hello world electron apps.
Web apps also don't necessarily mean someone else has control over your data -- it is technically easier to determine whether they do. You can inspect web requests in your browser, you can't in most native apps. There are plenty of silly things like Dark Souls stat calculators that make so much more sense as a webapp, and are 100% client side.
Why? there are better languages, platforms and layout engines. HTML/CSS/JS was meant to be a document markup sharing platform, not a rich application one. Use the best tool for the job.
These are intertwined with the language and GTK especially does not look attractive on macOS and Windows.
The appeal to HTML/CSS/JS is it's 100% agnostic to the platform, and can even be used as a front-end to a program written in a different language.
Well, Windows does come with the MSHTML control. Sadly for some reason they decided to version lock it at IE6 instead of keeping it up to date for applications to use.
There's no reason a similar system couldn't be built to deliver platform-native applications that run with full access to data you control and which call out to corporate servers only for situations where those corporations are going to provide actual VALUE that couldn't be had locally couldn't be made. It just hasn't been.