The problem is that the majority of IE6 users are not in a position to upgrade (the ones that are have done so already). There's no point in telling them or bugging them since they are not in control of upgrades.

For example, the NHS (the UK's largest employer and one of the largest in the world) is still using IE6:

http://www.guardian.co.uk/technology/2010/jan/22/internet-ex...

http://www.theregister.co.uk/2010/02/01/doh_ie6/