Why only one?

I listened to the last movement of the Grieg Piano Concerto on the way to work today, and was reminded again of what a monumental composition it is. Surely it is one of the most beautiful pieces of music ever written.

This raises the question of why Grieg wrote only one Concerto. If this one was such a success, why not duplicate the effort. I have no idea why, of course, but perhaps we can find the answer in considering other famous efforts in that field. Rachmaninoff wrote four Piano Concertos, but it is the gorgeous Second that we remember. Prokofiev wrote five Concertos, but it is the pyrotechnics of the Third that make their way to the stage most often. Maybe Grieg figured that if you have hit a home run, there is no need to go to the plate again.