Justin,
Some of it is the result of modern "necessities" which the old courses didn't have: wall-to-wall cart paths, deluxe irrigation systems.
Some of it is the influence of contractors: 25% profit on top of everything you do, and naturally they try to convince you to go the extra mile.
The rest is ego, whether the client's or the architect's, plus profit motive on the part of the client. Everyone wants to build "the best" nowadays; not many clients ask us to build a golf course for a reasonable green fee. Sad, but true. Even muncipalities get caught up in building "the best."