Possibly because Robinson doesn't have many high level guys in America, or if he does they're retired themselves and Robinson is practically retired which is why he moved to Little Rock, Arkansas to be nearer his son (as far as I know his son isn't a wrestler, but an officer in the US military).
There's a couple of American guys who were part of Robinson's UWFi Snake Pit in Japan. Billy Scott is thought to be the best American pro wrestler out of that dojo, I think he may still pro wrestle. He has a gym in Kentucky. Scott was one of Gary Albright's famous victims for getting full nelson suplexed unconscious.
The other that I know of is Robert Lucarelli, who was one of Seth Petruzelli's first coaches. Lucarelli is retired now even from training due to a plague of injuries sustained over the years to his back, hips and knees.
Since Robinson started his certification through Scientific Wrestling, I think back in 2008, he only has a half dozen or so assistant coaches, and no full ones.
So the base Level 1 guys are a bit like Gracie Garages I suppose, only Robinson is the only one who can certify you, and he won't do it online, it has to be based on watching you on the mat for hours at a time. I think a full coach certification requires at least 1000 hours with Robinson, academic knowledge of Catch and the theory, as well as proven ability to coach and compete (through video evidence).