But in fact I'm not sure that we see more Lisp use in startups, either. That could be because they aren't taught it in school. (Many startup founders haven't had the chance to pick it up on the job. For that matter, many programmers haven't had the chance to pick it up on the job.)
On the controlled experiment: Why was that? I mean, it has to be possible to rewrite anything in C++ (Turing complete, and all that - but possibly at the price of Greenspun's Tenth Law). Was it because the people who tried didn't know anything about Lisp? (Were they working from the source, or from the spec, or from the program documentation?) Were they just not as good programmers as the Lisp programmers (and don't say "if they were as good, they would have been using Lisp" - that wasn't their assignment). Did they have less time, less resources? Why didn't/couldn't they do it?