Perhaps the most obvious reason a top prospect isn't called up to the big leagues is he's simply not ready. For others, serious injuries have derailed their timeline to the big leagues, such as Miguel Sano (Minnesota Twins), Archie Bradley (Arizona Diamondbacks) and Addison Russell (Oakland Athletics).
Then there those prospects who are major league-ready but won't be brought up until mid-to-late June simply because their clubs want to ensure they don't qualify for Super Two status. This refers to their major league service time, which would allow them to become arbitration-eligible at the end of the 2016 season, as opposed to 2017. Gregory Polanco (Pittsburgh Pirates) and Andrew Heaney (Miami Marlins) are prime examples of this phenomenon.
As much as fans might want to see their teams' top prospects, a few who simply won't be in the big leagues anytime soon, regardless of injury or service time. Here are five:
1. Kris Bryant | 3B | Chicago Cubs
Just 12 months ago I said the Astros should draft Bryant as the first overall pick.