This is because some project once created an internal application with a web interface, which was tested with IE6. This application may be critical to keeping people happy (e.g. the HR system) or some unqualified bozo may want to 'cut costs' like updating apps to new browsers, so mandates sticking to a 'stable' version like IE6. And all future apps will have to target IE6 forever more...
It gets worse... People write apps that use Flash (online training) or Java applets.
There are solutions to this, but none of them involve using the one true SOE, one SOE to rule them all!