I could be wrong, but I think that the ankles for toris arent as strong/fast as they should be. is there a reason for this?

I think it's more the range of motion. It's like wrist joints, they can only go so far and when a certain degree of force hits them at the wrong angle or forces them over the range of motion that's available to them then they snap. It's simply because they haven't got a of flexibility like the other joints meaning it's easier for them to break.

If you lax or hold your ankle, they basically speed up and go straight through uke, which is how I personally get my booms. They're not weak, you're just kicking too much with the joint and not with the foot, if that makes sense ._.