He dismisses "lack of support for modern programming practice" far, far too easily. Clojure is modern. CL is not. That lack of modernity is a serious reason not to use it.
It is also specifically noted that Lisp programmers who use Lisp part time have right to write why they do not use Lisp - when they do not use it.
There is a huge variety of reasons and ways people think.
(I think the actual answer here is: mindshare. Respondents heard Lisp and assumed CL, maybe Scheme.)