In my view, it's not that surprising.
- Laver was 31, at the end of his prime, when he won his 2nd Grand Slam in 1969. He felt that he had nothing left to prove in the majors, and there may have been some animosity over his being banned for so many years in his prime, although I can't verify that. But, he continued to maintain a winning record in pro events against every other player, and was still regarded as the best player in the world, for the next few years. When the official ATP rankings started in 1973, he was ranked as high as 3, and remained in the top 5 until 1975 - while foregoing the points he would have gained by playing more majors.
- Like all dominant players, there's only so long even the greatest can maintain the kind of mental focus it takes to be the best. For 7-8 years, Laver was the best by a wide margin, in an era full of championship level players, and he did it longer than most. Look at Borg, Sampras and Federer. Because of the mental/emotional demands of the game, IMHO, tennis players burn out quicker than in any other sport. Laver's run on top of the tennis world was among the longest ever.
- I would also proffer, although I can't verify it, that Laver preferred to play the highest paying events in order to make money before he was out of tennis, rather than play for more prestige that he didn't really need.
JMHO, of course!