I am sure you are being downvoted for mentioning Betteridge. I upvoted you because using causation to describe evolution is inherently flawed. Discussing it in that framework only confuses the nature of evolution. Our ancestors didn't become bipedal "because" of any one thing in particular. None of our ancestors were sitting around saying "Hm. I wonder how we can influence our future evolution." "Well, it would be nice if we could throw." There were likely a lot of benefits to bipedal motion in early humans and that's why they out survived those on all fours.