USA Today has an interesting snapshot today:
Among golf’s major, the PGA Championship has produced the most one-hit wonders—champions who have won only one major in their career.
PGA Championship – 31
US Open – 23
British Open – 21
The Masters – 14
We can speculate that the Masters has the fewest because it’s the youngest. But by that logic, the British Open should have the most. It also could have something to to do with the fact that, from its inception in 1916 through 1957, the PGA Championship was a match play event. A single bad day eliminates you from match play, while in medal play, you still have a chance to recover.