I think the way he got most of his knockouts was his deceptive speed. Despite his build Hendricks covers distance really quickly, and often hits people before they can even react. That is what happened to Kampmann and Fitch, and when he hurt GSP in the 2nd round (but GSP showed good defensive footwork, posture, secured position with his low stance, both feet planted with the knees bent, to absorb the punch). You have to stay closer than you think against Hendricks. If you give a guy who explodes forward like that space to build up the momentum, he will run most guys over. He doesn't hit as hard when he can't step as much into his strikes, but then of course you have to deal with the wrestling and clinch game. The fighters Hendricks struggles to put away are either solid defensively (GSP), nigh-impossible to knock out (Condit, Brown), or both(Lawler)
I think the Lawler fights with how much damage he took, weight cut history, and recent changes to his training camp have contributed to his decline physically and technically.