It seems like they're balancing features with speed. In order to get a bunch of extra features, every page load needs to be 200mb of extra crap that 99% of users won't use 99% of their page views.
Oh and hamburger menus are hiding the key features you DO use every page view.
Why doesn't JIRA offer a native desktop app? Everyone using it is on PC, Mac or Linux right? And then a cut-down iOS (iPhone and iPad) app covers the rest?
A few colleagues use a Visual Studio extension, although that seems to be mostly handy for time-tracking and limited interaction with issues. It's also stuck in a UI that goes back to 2008, so perhaps rather fitting ;)
Oh and hamburger menus are hiding the key features you DO use every page view.