The biggest reason why Cormier couldn't get Bones down is because of Bones's LEVERAGE, his height and reach isn't just effective for his stand up, but also very good for allowing him to stay on his feet.
It's like trying to take down a tri-pod. He just has so much LEVERAGE and good enough wrestling to know what to do that for a short guy trying to take him down, it's almost impossible. The law of the LEVER.
Gus took Bones down via element of surprise, but mainly kept the fight standing. Gus has good stand up, but if (for arguements sake) Gus was the same height as Dan Henderson ... Bones would have f**ked his shit up real quick, regardless of stand up ability. Real talk.