I tend to view the reduction of high-school-age shooting teams as being largely cultural. The legislative effects of gun control did succeed in moving shooting facilities off-campus, but then again the ownership of, say, swimming pools and cars is also largely restricted to adults (admittedly less by law and more by expense).
Swimming and driving are activities one must engage in off campus. But surely if the rate of high-schoolers who drive decreases, we need look no farther than a cultural shift. It seems to me that a "media/public" conspiracy as Freedom1Man describes is really nothing more than a cultural shift akin to any other except for one detail: our own dislike of it.
It seems clear to me that the 20th century marked a low point in America's cultural appreciation for its 2nd Amendment rights. Alongside this, we find a high point in legislative attempts to restrict or limit civilian ownership of guns. (It's less clear which is the cart and which is the horse in that causal relationship; did the law react to culture, or did culture react to the law?)
It also seems clear to me that Americans are, to a large degree, beginning to once again appreciate the value of the 2nd amendment in a broader content. It also seems to me that the law is -- belatedly and incompletely -- moving in the same direction.
If I'm right in concluding that the direction of causality is cultural shift --> legislative shift, then it is also likely the low point experienced in the 20th century had the same causal structure.
Of course, one benefit of open carry is to effect social change, and I really do think it has worked; it is working (idiots with long guns in Kroger or at the zoo being the exception, of course). So I think the shifts will continue. Maybe we'll see a resurgence in shooting teams.