I certainly understand why kids go to pro ball right out of high school and don't blame them for taking the money. It's a jump start on their career and they get the opportunity to develop from a professional staff paid to get the most out of them.
I am, however, shocked at how low the bonus he was offered and took (unless it's being misreported). He fell to the 28th round because teams thought he was going to college or his monetary demands were too much for his value. The scounting report on him was electric stuff and could be a very high level prospect if someone taught him to throw strikes and put him in a good weight program. PG had him as the #3 RHP in Texas (in front of #4 Jack Conlon) which means he likely would have been expected to be a weekend roation guy if he developed properly. He was considered the 246th best prospect in BA's top 500. For comparison, Conlon was 239th overall by BA. If he got drafted exactly where BA had him, he would have been an 8th round pick. I don't know what information he was floating to teams before the draft, but I have to think if he was open with teams about signing he would have been drafted in the top 10 rounds and gotten a higher bonus (even if it was $200-$400k).
The tweet I linked mentioned him having some elbow issues so I don't know the full situation with that and how that may have impacted his draft status or his likelihood of turning pro. Maybe he didn't want to go to college and have a coach abuse his arm (not pointing at A&M specifically).