Popularity in industry seemed to be a big factor, with Java, C++, C# and Python making up most of the entries in the top 100.
Speed wasn't that important: Python made up 20% of the top 100.
Some popular languages, such as Javascript, PHP, Ruby and Perl did quite poorly. I'd blame it on speed, but Python did quite well.
New and exciting languages I'd expect the sort of people who enter programming contests for fun to like were underrepresented. Only 6 people used Go, and 4 used Scala.
Unless I'm mistaken, the contest was limited to supported languages. F#, Clojure, Lua and Scheme don't appear because they weren't supported, not because nobody wanted to use them.