Besides the fact that our good mongolian friend appears to be made of rubber, the main limiting factor there was that Mikey was wasting a lot of the effort by rolling and turning, which means none of that effort is going into the leg. You want to essentially eliminate any ability by the opponent to roll in the moment you are making the break, keep him stuck in place, and impart twist on the leg through your grip as you extend, or compress it with a side crunch. Mikey was doing a lot of pulling the foot across his chest, which is a common mistake even many otherwise very good guys can make if they are less familiar with heel hooks in particular, and is basically a useless gesture that only gives the opponent opportunities to escape.
For sake of comparison, see how it looked when Craig Jones broke Vinny Magalhaes' leg.