But why is it terrible? Just because it's a bulky, but cross-platform solution?

It uses ridiculous amounts of resources, introduces security issues (when you remove a bunch of the sandboxing a browser does, but then still execute content that comes from the web, bad things are gonna happen), and generally the apps don't conform to any desktop norms for any platform.

This is supposed to be a full-fledged IDE. Those tend to be resource hungry anyways.

Plus the interface is looking pretty straightforward and native to me - no bootstrap-ish/whatever website-looking-thing shenanigans disguised as a native application.