The question assumes a static environment, where existing and new courses of both classic and modern influences can peacefully coexist so that everybody's happy.
I think the spiffy water features fronting greens at George Thomas's BelAir CC shows that this is hardly the case.
painting courtesy of faegrefineart.com
The golf world, along with being made up of individuals, has a collective mentality that is influenced by trends and peer pressures.
Why did Aronimink turn their 1920s Donald Ross course into just another version of the RTJ Frankensteinian monster in th 1960s?
Why do clubs compete with each other to see who can hit the fastest stimpmeter numbers?
Why did most clubs in the middle part of the last century turn their open farmland into parkland nurseries through "beautification" programs?
Why, after Pete Dye built the 17th at Sawgrass, was the world inundated with replicas and takeoffs?
Why the latest arms race to keep building back, and back, and back and back tees to stretch courses out no matter how ungainly?
It's simply because like anything else, golfers are people, and people are driven by various motivations including keeping up with the Joneses, wanting to be stylish and trendy, wanting bragging rights in the neighborhood, being influenced by ideas, both good and bad, and copying them as they see fit.
What happened during the Trent Jones post-war era (probably beginning with his remodel of Oakland Hills) is that golfers en masse began to get a visual interpretation of what a golf course
should look like and everyone followed suit.
Today, the USGA would have us believe that doing much the same thing...pinching in landing zones, stretching the course to 7,500 yards, thick rough, wavy amoeba bunkers of glaring white, manicured sand, flattish but FAST greens ala Torrey Pines, is what a golf course should be.
People watch that stuff on TV, and all of a sudden their club back home with WIDE fairways, slower but undulating greens,
6,400 yards from the tips, and some raw hazards begins to seem seriously outmoded.
Next comes a new Greens Chairman, and we hire a modern architect....