One reason might be that I feel like Dawkins fans grew away from him whereas Hitchens had this punkishness to him that made him stick a bit better. Also he died early enough that his biggest gaffes

I fully agree with you here, I think Dawkins' incredible uncharisma + his number of public appearances undid him, but he is the guy who created Sargon, et al. As someone who briefly affiliated themselves with the Atheism movement, I always found Hitchens' writings to be threadbare and infrequent compared to Dawkins, who wrote voluminously on one of his great points of obsession. In 2006, I wanted to like Hitchens because I was told he was Cool, but always found him hard to grasp.

I think you're right though, if he lived even two years longer that punkishness would be 0.