It seems to me that as a position player Hitting is the tool that will get you drafted. Other tools are good, but hitting is king. A position player that can not hit for average and/or power unless he runs 6.3 and has an additional tool, will probably get passed on.
For pitchers, it is obvious that velocity will get you there, even with minimal control or additional pitches. I guess that the belief is that the rest can be taught, But hitting (batspeed), running, and armstrength, seem to be God given skills that otherwise are not easy to develop.
If a kid can drive a ball out of a park with wood against decent pitching at 18, even if he does not do it consistantly, shows a skill that is not easily (or possible to be) taught. Temper flare ups because of unmet expectations may infer desire and an unwillingness to accept mediocrity. Some maturity may help with these mental lapses. The ability to hit consistantly can be developed by a player who already has the gift and the skill to hit.