'If It Ain't Broke, Don't Fix It': said by IT departments everywhere responsible for the prevalence of old browsers versions in enterprise businesses.
We did look at some cheaper options, but it's interesting that the manufacture of electronic systems doesn't really have anything cheap in the space. Properly managing nested BOMs of an arbitrary depth? Pretty much always a high pricetag or something you have to hack yourself...
IE6 just becomes the shell to the webapp instead of a browser in its own right. MS probably even has a way to install multiple versions of IE concurrently so you could run IE6 + "modern IE".
On Windows I think the official way is runnng it in a vm.