Or perhaps they tailor their product to demand.
There is a demand for IE.
I use other browsers about 99% of the time, but I also need to have IE installed.
A home user might be able to get by with it, but I use a grip of different management tools, some of which require IE.
Some router config utils don't render properly in FF (and some don't render properly in certain versions of IE.)
I'd be pretty annoyed if I was doing a new office setup and couldn't install network devices because I needed to download a browser first. Not because it's a huge hassle, but because it an unnecessary one.
You can whine ad nauseum that it shouldn't be this way - but it is.
On my home pc's, IE is installed, but isn't the default, and the shortcuts are deleted.
The only way it runs is if it's started from command line or Start/Run.
To program is to be.