Bobby Jones started it back in 1930 when he won the original slam, the U.S. Open and British Open and both the U.S. Amateur and British Amateur. That became the standard. At one time Jack Nicklaus said he would never turn pro and that presented the possibility that he could equal Jones' feat, but Nicklaus soon realized he wanted and needed more competition than amateur golf offered. When Hal Sutton won the U.S. Amateur at the Country Club of North Carolina in 1980, his father said Hal was going to remain an amateur and his fondest wish was that his son could match Jones' slam. One year later Sutton was a pro.
Professional golf offers too much for a superior player to pass up.
For that reason alone, there never will be another Jones Grand Slam. Arnold Palmer realized this. That's why he invented the modern Grand Slam. Arnie and the late Bob Drum, a sportswriter at the time, were flying to Great Britain in 1960. Palmer had won The Masters and the U.S. Open and he was hoping to add the British Open at St. Andrews.