There really isnt any question that is why. He has been eyeing the gub job for a while. having to defend Trump for 4 years would make it much more difficult, as his town hall proved.
Basically the same reason that Romney did not run for re election as governor when he wanted to run for president.
IMHO, Chaffetz is a phony, hypocritical self-promoter. Doesnt have an ounce of integrity, as everyone who has ever worked with or for him will tell you.
somehow I hope Spencer Cox beats him for the nomination.
So I said to David Eckstein, "You promised me, Eckstein, that if I followed you, you would walk with me always. But I noticed that during the most trying periods of my life, there have only been one set of prints in the sand. Why, when I have needed you most, have you not been there for me?" David Eckstein replied, "Because my little legs had gotten tired, and you were carrying me." And I looked down and saw that I was still carrying David Eckstein.
--fjm.com
http://www.cnn.com/2017/04/20/politi...-house-resign/
I'm wondering if Chaffetz has seen enough to know that Trump is going down over the Russian ties, and so he's getting out before he has to be a part of the investigation and impeachment. If the evidence against Trump is as bad as some say it is, there will be no place to find political cover for Republicans.