Earlier quoted context omitted.
The problem is internal legacy applications that only work in IE6. If they upgrade browsers the apps break, so in order to support these apps they keep IE 6. The question for them is 'do we spend time and money to update all of our applications to upgrade a browser, or just leave things the way they are for now?'
Sometimes the question isn't even "do we spend time and money to update our applications", because sometimes the code for the applications is long gone, along with the company that wrote it, and all they have left is the compiled code running on some server in a back closet.
We're in a recession now. There're a bunch of unemployed web developers. Let's simply ban the use of IE6 and kill two birds with one stone! Break some windows and burn those diskpacks, baby!