Earlier quoted context omitted.
The pay might be high but the average career is much shorter than that of a programmer. I bet the lifetime earnings aren't even that much different than the average person checking HN from California.
Average MLB Career is 5.6 years[1] * $3.8M/year = $21.28M Divide that by 40 (assuming a career from 25-65) and you still have $532k/year. [1] http://www.ramfg.com/RAM-Financial-Group-Solutions-Professio...
So in pursuing professional baseball, you really do open yourself to a significant risk of finding that you're 26 and spent the last five years making very little money and now you don't have a job, or any professional skills beyond the offseason job you may have worked.