I read an article on McCutchen's journey last year and basically a coach saw him play and thought that he needed to play on a higher level to reach his full potential.
His parents were hardworking folks by all accounts but couldn't afford travel ball. Also, due to their work schedules, they rarely got to see him play. The coach and other basically sponsored (travel, hotels, food, etc.) him throughout the summer.
In this case, as in many others, it was simply a lack of resources. If others didn't make a decision to help him, he wouldn't be where he is today.
I know a player in basically the same situation. Extremely talented kid but parents don't have a ton on desposable income. Sometimes folks are willing to step in and help but it doesn't always happen.