The Pirates are completely inept offensively. They've developed some pitchers, found some real gems in FA, but their ability to grow hitters internally is as big an F grade as you can give a franchise.
Davis is well on his way to being a monumentally bad bust as a 1 overall. When you're as cheap as the Pirates, you can't afford to miss on that kind of pick. Even if the guy doesn't turn out to be a star, you need an above average league player and HD is just completely overmatched at the ML level.