It's a tough choice for a kid (or any of us). And frankly for most it's not about the money. They've dreamed their entire life of being a professional baseball player, and then a team sets their dream in front of them on a table. All you have to do to realize your dream is sign your name. You don't think about 2-(eternity) years of bus rides, hotels, and living paycheck to paycheck, you see a chance to play in front of 40,000 on national TV and you get the chance to start making progress towards that NOW.
Frankly it's probably a harder decision for a 28th round pick than a 3rd round pick. If you merit a 3rd, you're probably pretty sure you're going to go to college, be a weekend starter, and then get lots of exposure. If you're a 28th on a great time then you may have to languish in the pen for a bit, pick up scattered innings here and there, and hope to earn more playing time. In the minors you have greater access to more coaches/trainers/staff, and you don't have classes or NCAA mandated limited hours for practice.
I wish he had chosen to come to campus, but I can't ever hate on any kid for choosing to take an affirmative step towards their dream when it's placed in front of them.