When I finally got a job in High school, after which I had money to start flying something other than the Cox plastic jobbies and Free Flight airplanes, I started with RC airplanes. Later I graduated to Control Line airplanes. Now I fly everything, FF, RC and Control line from sport ships to pattern, scale and Combat. I've got a cute little asymetrical 1/2a powered ff helicopter that has given me more joy than most of the other aircraft I have. And as far as RC is concerend, I am Mr Clean of RCCA Combat fame. Yup, world famous in Missouri anyways, I've done it all and still do.
But I've swapped back to flying control line for the last couple years. I actually wouldn't have gone back to RC if I hadn't moved to a town where the people who were flying CL were so spread out we never got to fly together. It's just not the same. RC IS too much like a video game. I can get more thrill out of flying a simulator and thanks to my SPAD connections rebuilding is just about as fast as a simulator

RC combat made sport flying just about pointless and not exciting. I do fly off water once or twice a year, that's kinda fun. But really it's just an excuse to go hang out with my buddies. When I fly CL, I work at the pattern, or I help others get up and going or give check rides to kids in the park. Nothing I ever did in RC is as fun as getting up in a mass fly of more than 5 people in the CL circle, now THAT's fun. I must admit that if I lived closer to a good slope it might be hard for me to choose between slope flying or CL, but eventually my love for those little engines would win me over. I love the smell of castor or the perfumed smell of synthetic oil. Gotta love throwing your airplane over the edge and flying till the batteries go down too, hmmmm.
This is like asking someone why they don't move off Golf and move up to Tennis. No, this is like asking someone why they don't move up from Steeple chase to Polo, yeah, both of the them use horses just like both RC and CL use airplanes. The airplane is really just a coincidence, the two have many other differences.