Pat,
I would think that from 1929 to 1947 .... it was pure survival for many (most?) courses and architects. Bunkers went to grass or were plowed and seeded. Greens shrunk. Many courses folded. Not very many changes by members or architects.
Then post WW2, late 40s and early 50s, it was probably as some mentioned....tennis courts, pools, etc. A part of that in the early 50s to 1960s, perhaps led by Oakland Hills in 1949/1950 for '51 Open (I brought this monster to its knees or such) brought many architectural changes to classic courses.
From C&W, for RTJ alone, RTJ alone, a quick partial listing indicates the following remodeling. This doesn't indicate what was remodeled but that many courses were being 'improved'.
CC of Birmingham, 1959
Olympic, 1954
Broadmoor, 1954
Ponte Vedra, 1954
ANGC, 1950
Burning Tree, 1963
Chevy Chase 1948
Congressional, 1962
Detroit GC, 1953
Oakland Hills South, 1950, 72, 84
St. Louis CC, 1952
Century, 1959
NGLA, 1959 (?)
CC of Buffalo, 1954
Oak Hill East, 1956
Siwanoy, 1953
Winged Foot West, 1958
Charlotte CC, 1962
Firestone South, 1959
Cascades, 1961
Belle Meade, 1957
Colonial, 1960
Mid Ocean, 1953
Southern Hills, 1957
This is just a short list for RTJ. There were other architects out and about. I would imagine many had no frame of reference to the classic period owing that to the depression. Golf architecture was probably not a viable venture for most since there was no growth and probably a shrinkage in the number of courses.
Those few architects, who made it through to the other side of depression and WW2 and had a reference, were apparently bent on modernization to their ideas.
The club leadership was probably also ripe for changes, given the membership approves of all architectural changes ! Lets say you were 45 in 1928, an important founding club member who selected the architect, and by the time the war was over and economy picked up, you would be 65 or so and out of the club loop by the time all the young veterans returned. It was the 1950s, TV, cars, and more cars, planes, and everything could be made better. Club leadership probably had no reference to the classics.
I think Ron Pritchard made a good point. There was a lack of reference and the very few (or a few key archies) who did have a reference chose a new modern approach as some pointed out earlier.