TEPaul,
In our conversation this morning I indicated that I felt that several factors conspired to narrow fairways.
Item (b) as outlined by Tom Doak above.
The prefered flight of the ball, a low draw.
The equipment vis a vis Paul Cowley's response,
The huge fairway gang mowers which needed tremendous room to turn
The new single line irrigation systems.
And, lastly, the need for clubs to cut costs as they went through difficult times.
Today, you might want to add the cost of real estate as a factor.