Back in the days between the two, drawing was the more accessible hobby simply for the fact that all you need is a pencil and a drawing block. Apart from the analog point-and-shoot cameras, the professional ones back then were expensive and requires film (which can hit you like your car petrol bill). It used to be quite common to see parents taking their kids to drawing classes, where you would see them rushing out to their parents at the end of the lesson, proudly displaying their magnum opus to their bewildered parents (I was one of them). This was prior to the age of tuition classes and golf lessons for kids.
Now with the digital revolution of limitless shots (read: camwhor-ing with QC) and online photo albums, the art of photography has really overtaken the art of drawing, entering into the mainstream. Throw a brick from a window and you'll most likely hit someone with a SLR slinged over his/her neck.
But I think deep down it has probably got something to do with our lifestyle now, in which all things have to be swee swee and chop chop. Why take the time and effort to do a portrait or a mural when you can get instant beauty with a click?