Sounds like Ashcroft worked really hard and then got sick. He's probably all worn out. Don Evans PROBABLY can make a lot more money in the private sector. That's my theory on their departures.
I think the money is one of the main reason they leave. I know that I heard that Tom Ridge would leave for that reason. The other reason would be, for the ones that have to go before Congress very often, is it isn't worth the crap they have to put up with.
I think Don Evans is sick of the culture of DC. He's a good, honest man and it must be very difficult for him being away from the more wholesome atmosphere he comes from.