He's too busy, important to come on plop, too big a deal. Doped up horses and cheating, without that he's who. 
He is an excellent driver. Tactful, works out a trip, doesn't abuse a horse, good on trotters, good on young ones.
Yeah he does drive for some people I wouldn't classify as high on the integrity list, but so do effectively all upper-level drivers. Not saying it's right, but he can improve a horse without pharmaceuticals based on talent alone.