We use a true random, not an even probability distribution: so it's possible for all sorts of unusual things to crop up in worlds without it being broken. The same is true with AI War, with lots of stuff that seems highly unlikely but actually is quite valid to happen. This definitely falls into that category.
However, if you've been using seeker enchants to get something other than leg enchants, then that could account for it; wearing a right arm seeker enchant could lead you to getting almost no leg enchants, for instance. If you're really after a double jump enchant, I suggest a leg seeker enchant as the remedy. It's not a surefire thing -- true random after all -- but it would certainly raise your odds substantially.
The natural human tendency is to assume that when events are random, there will be an even distribution of results. That might sometimes tend to true over infinitely large sample sizes (I forget now at that scale what happens), but at human-scale sample sets it instead trends toward "statistical clustering" and other irregularities. But only some of the time! No clumping at all is something that can happen with some good chance, too.
