Mostly b/c they've promoted the top prospects, the rest are probably guys who won't make waves for a year or two, if ever.
Normally a guy like Tait would be in the DSL at 18, instead of FCL at 17. And they just promoted surprise of the season, Ferrebus.
Most 17 year olds play sporadically, the focus I think is on skills instruction and strength training the first year in the organization.
Pitchers tend to take longer, a position player who isn't stateside by 20 should be thinking of an alternative career.