The crucial difference is that on Facebook, you see people actually talking (and tagging) their friends who are Crossfit users, which in turn drives up the video viewership and final counts. On Facebook, comments drive distribution. On YouTube, you want to duck for cover.
YouTube comments are, rather infamously, a cesspit of hate and adolescent humour. Linking them with Google+ has done little to improve that. Meanwhile, Facebook have found a solution for making video truly social.
Time to take another look at Facebook video.