Wayne,
Most sandy areas will become grassed in naturally over a period of years, even in northern climates. Also, golf course superintendents are not too fond of sand blowing onto their fairways and greens, or erosion in their bunkers, so they tend to want to grass over waste areas.
I think it was likely one of those causes, instead of play and rules issues, which saw the transformation. On top of those, sandy wastes just weren't the norm back in the old days, and all courses tend to gravitate back toward accepted norms over time. Even, sadly, Pine Valley.