The problem isn't always a lack of IE8. Government agencies often have a forced group policy that puts IE8 into "compatibility mode" so it's effectively IE7... which is only slightly better than IE6.
Many still have IE 6.0 on XP SP3 ...
It's fully supported by MS.
It's in extended support but out of mainstream support by now. Just as XP.
Well, not really. IE6 is essentially dead. Throw out a few Asian countries and the market share will drop significantly.