For the broader advancement of the game of golf, shorter is undeniably better. I can't imagine how frustrating it must be for beginners to try to hack their way around a "modern" course of 7000+ yards with modernistic hazards, even if they play from the forward tees! As Tom says above, not only are shorter coures more accessible (skill-wise) to the great majority of players, they can be played quickly and enjoyably, which just has to make the game more attractive for repeat play.
It is true that shorter courses can be boring to big hitters, but they also frustrate these players, which is good for deflating their egos. My home club (par 67, 5472 yards) held a scratch tournament this weekend, and with no wind and soft greens only one of the 44 low handicap players broke par.
There is a need for 7300+ yard courses, given the (lack of) distance control measures by the R&A/USGA, but these courses should be only 1% of the total built. It saddens me that some of the best pieces of land for golf and a grossly disproportionate amount of the considerable talents of some of the greatest modern day architects of golf are being dedicated to these monstrosities, rather than to courses which will allow the 99% of us to better enjoy and play the game.
Why?
Follow the money, and the egos........