Devil's advocate here, but this is kind of chicken or the egg. Meaning, are these guys D1 players because they participated in travel/showcase events? Or did they participate in travel ball/showcase events because they are the top players and that is the new norm/expectation?
I guess more simply: if none of these guys participated in travel/showcase, how many would still be playing Division 1 baseball?
In many respects the showcase recruiting phenomenon is a reflection of how the world works today. Industries of any size tend to build around a pool of talent and resources - Wall Street, Silicon Valley, Hollywood, etc. These nuclei then attract more talent and more resources until they become "the place to be" if you want to be successful in that space. The concentration of resources and competition makes recruiting in these hot beds a no-brainer. Baseball is no different. Sure there's always going to be an actress discovered in some small town USA, but for most it doesn't work that way.