I'm with you - what's ultimately important is wins and losses at the big league level. However, baseball teams are businesses who look both to win games and make money. Although they don't adhere to every tenet in classical economics about profit maximizing behavior, they still operate on budgets. No one in real world management can ignore the costs completely. If you were to sign Glavine, Colon, Pedro, Burnett, and Zito to free agent contracts, how would you have money left to sign position players? Moreover as you point out, guys who sign get hurt, and then you've wasted money. Not every prospect pans out. The vast majority won't sniff the big leagues, and fewer still will make a significant impact. However, building from within is absolutely necessary for teams across the pay scale.