Those distance gains haven't carried over to this 62 year old amateur.......
I do recall following Jack Nicklaus when he played with that Golf Digest Contest Winner. He went on and on about how he hits a 4 iron further now (this was 2004) than in his prime, but even some of his people whispered that he liked to ignore the extra inch of shaft length and fewer degrees of loft that essentially made it a 2 iron.
This study is a bit different in that it compares actual driving distance from then and now, not comparative clubs. I know a few years ago I played La Costa with Steve Pate, and he was still only driving it 270-275. Granted, sea level and cloudy, but I don't think he picked up much distance.
It's also interesting that he picked 1990 to compare, which is just a few years before the intro of the Pro V 1, which is where the biggest jump comes from. John Daly was the first pro to average over 300 yards - and that was 1997.
Some other differences could be the harder fairways, as noted, easier course set up that encourages swinging for the fences, and my favorite, extreme club fitting which can really increase distance, especially roll. That seems to be where most of the gains come from now days.
and that(constant justification and different "interpretation" of data) is why no one has noticed...until recently...the massive gains.
But then more distance gains equals more work for architects and builders.
Jack Nicklaus hitting ANY souped up 4 iron at age 64 farther than his 4 iron in his prime of the 60's when he was a distance monster should be enough but justify away.
Steve Pate-driving it 270-275 at la Costa-as a senior-is actually quite significant.
years ago on tour they used to drive it 235-250 there as the air, sea level and soft conditions really hurt tour averages-and the averages never really got normal until they left the west coast and got better weather and firmer ground.
1990 is not really near 2001, when the ProV1 actually came out-though distance gains were made with the Titleist Professional as well.
While you are correct about clubs being optimized for more roll now, carry distance is insane for TOUR players.
Rory was carrying the ball 365 on the range at the PGA and they all carry it 280 or more.
years ago 240 was a long hazard to carry and 260 carry was reserved for Nicklaus and a few select bombers.
Averages aren't really the best way to measure gains anyway as course lengthening and safe landing zones have not kept up with distance gains so many tee shots are not drivers.
I close with Freddy couples at 57 or whatever, averaging 300 vs. 272 at age 30.
Fitness gains? seriously