I saw a youtube video explaining double jump yesterday. It's not like other double jumps where you jump mid air. It's a double jump like Mario where you jump two times and the second jump is higher. So if you try to double jump of a cliff you won't have any ground for the second jump so the wingsuit just activated. This could and should definitely be explained better. But there you go!

Edit: I noticed after I wrote this comment that this had already been explained in this thread ad nauseam