1. Cutbacks of "scheduled creativity" time at school. This is a HUGE one. In the 70's, my school had an art class, music class, plenty of PE. Now, that's hugely, hugely cut. If I want my kid to do art? music? sports? (she wants to, after all). After-school scheduled activity time!
2. 2 working parents. We're pretty free range, don't need to hover over playing kids, but we need to be within walking distance (at home down the street, or whatever). Juggling that "freely" as opposed to strictly-set activities? Much harder. Even if you get 1 afternoon free a week, there aren't other parents to trade off with.
3. Basically, chicken-and-egg. If my kid doesn't have anyone to play with because they're all off at activities, better to have them doing these activities with their peers than sitting at home bored and idle (not that some down/idle time isn't good, but there can be too much).
Can't think of ANYONE in my peer group who's worried about college for their kids yet. Maybe in a couple years.