It's not that it isn't enforced, it's that the rule is very specifically that it must appear that one foot is always touching the ground when watched in real time with human eyes, the rule isn't that one foot must technically always be touching the ground.
That very well may be the rule, but you can't then argue that it isn't a "silly way to run". It clearly is if both feet can be in the air at the same time.
I completely agree, especially with the "silly" part!
There is also a rule about a straight leading leg. That puts a limit on the leaping. A leg not being straight is pretty visible.