Ok, not really my field of expertise and there are people on here who will understand it much better than me but anyway:
1. Dimples on a golf ball are not about reducing drag as such, but about 'flow separation'. That is, how the air leaves the ball as it passes over it. I think.
2. On an F1 car, a similar effect is achieved using vortex generators on the ends of the wings and bodywork. Usually these are serated edges or winglets.
3. A golf ball spins as it moves in the air and separation occurs at different points, so the dimples need to be placed all over the surface. A car or bike moves through the air in a more consistent way, so separation generally occurs at the same point (say the edge of the wings or bodywork). Therefore, you only need to add the vortex generators at those points.
So effectively, this technique is being used in F1, but in a different way. I'm not sure about MotoGP, I've never noticed any vortex generators or anything like that on the edges of bodywork.
Clear as mud