I think before they can extend the grass court season, national tennis associations around the world have to provide more grass courts for clubs etc. to play on. Also, before there can be more major tourneys on grass, there has to be more plain ATP level tourneys on grass. It would be a bit disproportionate if there was, for example, a slam and a masters on grass and only a couple of other tourneys on grass...
Having so many grass courts for clubs is not feasible. They are too hard to maintain. That's why hard courts are most prevalent. You just can't maintain grass courts and play on them every day.
