I think I read somewhere that he historic reason that California had no clay courts was water, or lack thereof. No one wanted to waste the amount of water it would take to maintain a clay court. That, combined with a very dry climate which promoted evaporation. That was the primary motiviation behind the hydracourt system which waters from underneath by allowing the court to wick water up to the surface.
I'm all for more clay courts. Growing up on them, I did not, makes for a more complete player. Federer, McEnroe, Borg, Edberg, Becker (all clay), and most every other pro in the history of the sport grew up on either clay or grass. Agassi was/is the anamoly with his roots going back to hard courts.
I think the issue in the US is the USTA. They are the ones who really push the hard court agenda. If the US Open was played on clay or grass, there would naturally be a supporting network of tournaments on a like surface to support the Open. The pros use those tournaments to get ready for the Slam. And, there would be clay or grass tournaments before and after the Open. The same is true of every Slam.
I lament the passing of the US clay court season as it was one of the best around. IMO, green clay is probably the most fair surface going. It is consistent in as much as you can't build one faster or slower like a hard court. The surface speed changes with the amount of water and likewise will change during the course of a match, but it's a great surface.
The other big factor is the amount of injuries that the players are sustaining now. I think that the powers that be in tennis will have to address this sooner than later. If they don't, then tennis will begin to lose stars or run less events to help mitigate the loss in players. From a Grand Slam historic standpoint, hard courts have not been around all that long, the US Open went to hard in 1978 and the Australian in 1988(?). The amount of hard court tournaments went up drastically following these events.
IMO all Grand Slams should be played on natural surfaces. This would leave the much shorter indoor season for hard courts.