Animal Mother - It's because your leg entanglements are bad. Look up Reilly Bodycombs videos, he's got great fundamental leg positions.This is really important for leglocks; the straight ankle is my best and favorite submission.
If your leg entanglements are solid and you get comfortable transitioning through them, you can switch from one leg to the other when they defend repeatedly and eventually shake something loose.
The biggest thing for me is squeezing my legs right together whenever I get the leg entangle started; for a LONG time I was only focused on the sub and would have my feet tight but my knees and thighs would be relaxed. When I started concentrating on really squeezing my knees together to clamp down on their leg I had much better control AND it makes the locks much, much tighter.
