There are only 2 reasons IE6 is still around: those who can't, and those who won't update it.
The former are the corporate crowd for the most part who have fantastically complex intranets that don't work on other browsers - even IE7/8, either because they are horribly broken in terms of layout/rendering or because they depend on ActiveX controls that haven't been updated.
The latter is, by and large, the non-technical user with the years-old computer that checks emails once a week kind of thing and doesn't realise it needs updating.