It's a "security" thing. Big companies pay Microsoft money in order to have a "secure IT infrastructure" that "regulators" will like. Microsoft's lawyers wrote some words that appeal to those folks. Google's stuff is free, and so Chrome doesn't come with any guarantee that it won't single-handedly take out the company's entire technology infrastructure.
Obviously this is very far removed from reality (you can read Chromium's source code and audit yourself. IE? Nope.), but these people aren't operating in the real world. IE is the best browser for the imaginary world that the "decision makers" live in.
(On my work machine, running chrome.exe causes an alert to be triggered and execution is denied. Of course, renaming it to not_chrome.exe allows it to work fine. Secure!)