Back problems limited Nicholas time in the senior tour to the point he only played the majors in later years (Masters, etc.) where he has a lifetime exemption due to being a past champion of all four. Nicholas has made far more $$$ designing golf courses in his later years.
I remember just a few years ago Couples was leading the Senior PGA Championship in the final round over Bernhard Langer when his back went out and he had to have two people more or less carry him in to the medical tent, ending his tournament!
It amazes me that Fred Couples still plays golf. On a good day, his body alignment is rather tilted.