Sea the Stars retired - why now? Is it all about stud fees & not the sport of Racing with exceptional 3yos now?

I was very surprised to read about this. He is sound and fit, but owner Christopher Tsui and trainer John Oxx said they thought he had done enough for his career. I think they are expecting big stud fees, but where he will stand and the amount he will stand for has not yet been determined. I guess it is just another disappointment in the sport of horse racing.