"Surely everyone experienced at these competitions would quickly figure out that lisp et al are huge competitive advantages, and everyone would quickly switch."

You missed the part where I pointed out that current major competitions don't accept arbitrary languages. That's the key point of my post. All else is not even. If they did accept arbitrary languages I would accept your logic, given sufficient time for network effects to wear off.

Otherwise, if you're going to argue that it's the people and their experience that really matter, you reduce back down to my point, which is that all the experienced people have their experience in C++ as cost-of-entry to the major contest sites and thus tended to use C++ as the language they have by orders of magnitude the most experience in by virtue of it being the only sane choice of the ones actually offered, rather than any intrinsic advantage C++ has over the non-offered languages.