That's because most companies are not technology companies. They purchase all of their IT infrastructure instead of building anything in-house. So if the vendors they buy from only support IE6, their customers will be stuck with IE6 until the vendor decides to upgrade or their customers go with someone else.
It's worse. Most of the time the companies buy these locked in software, then the vendor goes AWOL and nobody can fix the mess, so they just try to stick to it until it horribly fails.
IE6 still has extended support with XP, but in a few years things will be very bleak for some of these companies.
But it's not all bad, some enterprises have a modicum of reason, solve the problem and at least try to avoid getting in the same mess again. At least that's the trend I perceive.
