Because it would be really great if they did!

Why would they? Making the website run well on touch devices and low-res screens is a better goal - considering that would run on any device.

Of course, the current site is horrible on touch devices and small screens, but that's an easier fix than building largely useless applications for multiple systems.

frankly all they need to do is fix the hover drop down menus at the top - logging out is not possible without committing the url to memory! everything else you can get to via one method or another but hover events (usually) drop downs on touch screens just dont work...for obvious reasons.