I think JK does make a good point here, but there are other points to consider when evaluating this. Look at what was available to up and coming players in Jacks day vs now and last couple of decades?
1) First and foremost the primary feeder tour, which didn't start until 1990, (currently Korn Ferry Tour) - Instead of being isolated Teaching Pros, the set of "next best" golfers can hone thier skills, like the minor league system in Baseball.
2) PGA Asian Tour - Founded in 1995. Where most of these players once had little to no opportunities, the Asian market is currently blossoming with top notch talent.
3) Other Mini tours, many of which I'm guessing have only popped up after Jacks prime.
4) Mature college golf programs with generous resources at their disposal for practice and instruction and frequent country wide travel to play the best competition.
5) As JK points out, superior equipment with advanced instruction techniques, technology, and data analysis to fine tune swings, ball trajectory, etc. much earlier on. Think of all the players who perhaps stick with it now at early ages instead of getting frustrated learning the game and drop out before they have a chance to develop into who knows what.
5) Junior golf programs, where players learn to deal with competitive scenarios much earlier on and are that much better by the time they reach the college and top AM ranks.
6) A much wider international advertising and promotional reach among the top golf bodies that transformed low profile golfers into high profile celebs attracting more talent to the game.
7) Current Tour card structure vs predominance of Monday qualifying allowing players to set schedules and in general establish better stability.
The relative ease and increased frequency of international travel allowing the best players to congregate far more often.
etc, etc.
And its not just Golf. NBA and NFL teams would decimate those from 40-50 years ago....