Then why did the Astros reach for Castro instead of obvious higher-ceiling guys like Bux, Gausman or Zunino?
Teams do draft for needs. The needs being shoring up weaknesses in their system, not MLB team.
Boras pushing to sell him to the Nats, according to several sources on Twitter (digest with salt). Could be true though, because there's no other way he doesn't go top five.
That's not the point at all. Signability is the problem. Boras wouldn't blink to send a kid to play in an independent league if he doesn't get what he wants, and with specific slotted amounts, that magnifies signability issues a lot more.