This is not hard to explain. As is so often the case, an altered economic situation has driven changed behaviors.
Twenty years ago, Legion was king. Then, a few people like Bob Williams and Jerry Ford figured out that if they could create quality venues that would attract many top players, scouts and recruiters would flock to see them play there.
This was a particularly attractive development for college recruiters, whose schedules and budgets have always been tight. Instead of traipsing to every local Legion venue, they could target a handful of showcases that attracted players relevant to their programs and recruit much more efficiently than they once had.
Suddenly, coaches of high school-aged players all over the country were organizing teams to travel to the increasing number of showcase tournaments; and they were drawing their recruits from the ranks of local Legion teams.
All one had to do to see the effect was attend a Legion game and a quality showcase event. The Legion game drew a handful of recruiters from local colleges and, perhaps, a couple of local area scouts or "bird dogs." Meanwhile, it was standing room only with scouts and recruiters behind the plate at quality showcase tournaments.
Not that the showcase movement hasn't led to some notable and lamentable excesses; but, at the end of the day, it's the more efficient way to see and evaluate talent (by far). Once again, Adam Smith's "invisible hand" has won the day.