Is that because there isn’t much ‘movement’ left anymore that one could leave? 
Already retirement of Dembski, departure of Luskin, the Brazil fiasco (with Behe repeating old lines as if new ones aren’t needed). Denton is there for the paycheck (having been the one who woke Behe up with his misnomer crisis talk), not for the Intelligent Designer, as far as rumour has it. The ‘ID community’ has lost momentum; that at least cannot easily be denied.
The answer to the title question is easy: Why do IDists criticize TE? Because it splits the vote, and away from their favour. They are minorities and will remain that way. They tried to ideologize with Intelligent Design, but have largely failed. Their conceptualistic game is up. Outside of the CSC’s few novelties with Intelligent Design Theory, the other links, historical and philosophical with creationism are too obvious to ignore and too easy to point out.
It is just no longer fresh and can’t be much fun to be an IDist anymore. The best ones don’t.