Because NOBODY is supposed to gain root permissions. Period. You need to use one a variety of hacks or exploits or R&D modes to do this, and it's simply assumed you know what you're doing at that point.

The primary problem is that attempting to upgrade a running application framework will fail, destroying the existing one, preventing any sort of bootup. In order to avoid this, it's necessary to use a serial console or apt-get over a non-running framework, such as updating one stored on an mmc chroot-ed in from one running on flash.

It's not NOT showing destructive packages, it's ONLY showing packages explicitly vetted for end-user use.