because Cashman hates prospects and they follow analytics to such an extreme degree that even if someone was on their game they wouldn't trust it. Even when our own guys do well, they'll attribute it to luck.
They'll never be able to develop anyone capable of 180-200 innings because they don't believe in variance and outliers. On top of that, we've seen this since Joba, they don't know what to do with pitchers with big time stuff, so their solution is eventually just put him in the bullpen so they can use him more even though a starter who can navigate 6-7 innings with that stuff is more valuable.