Our society, instant satisfaction culture, throw away economy, may not instill the qualities that make for successful modelers as much as it once did. That statement right there sums it all up in a nutshell. However, let's not get too carried away. Back in the "good old days" (remember, I'm of the new generation), there weren't very many modelers either--for other reasons (way more expensive than today, required much more building, etc.). Today, the hobby is much more accessible to the masses. Therefore, anyone with little $$ and time can try it out, and often do. Problem is, it isn't for everyone (for many of the reasons that you mentioned above). So, people move on, and drop their AMA membership. The difference between yesterday and today is the advent of cheaper technology, and ARF's. This allows more people access to the hobby who otherwise wouldn't ever give it a second thought. So, those people buy their stuff, get their AMA #'s, stick with it until they crash, or lose interest (whichever comes first), then drop everything (including AMA), and move on.

As a matter of fact, I think that the younger generation will actually be the resurection of this hobby (I'm modestly including myself in that statement). i'm not young, but not old either. I say that because this generation has grown up controlling things with their hands on a joystick (insert jokes here). This lends itself to a much faster learning curve than ever before. What can we do to help foster a growing enthusiam for the hobby?
I think we can do several things.
First, get young people (school aged) involved. many would be interested, and eventually make it a lifetime hobby.
Secondly, encourage them to do what interests them (i.e. 3D stuff, or helicopters, or whatever) even if you don't think it's "real flying."
Thirdly, don't act like complete butt's to the younger guys when they come to the field.

There are others, but you can see where I'm heading with this. Encourage younger people, and help them get into the hobby. Some will stick, some won't. That's life.....