One thing to consider, at some of the more expensive civilian schools, ROTC grads can have considerable debt, despite the full tuition and stipend. My sons were considering one school which took away the rest of their FinAid when they found out they'd be getting the ROTC scholarship for tuition. It would have meant $12K+ debt per year for each kid. That's almost $50,000 in debt they'll not have when they graduate USAFA.
Also, they wanted the full experience, like Christ Corps said. They didn't want to just show up for an hour a week and a few weeks in the summer.