So that's just 16 half-liter donations, which spaced out every 8 weeks takes less than 2.5 years. There's plenty of time for Dad to donate that much between when he learns his wife is pregnant and when that kid needs to enter high school. (Plenty more if Mom donates, too.)
The big problem, as in everywhere else, is that paying for blood attracts donors with bad blood (literally), some of which will escape testing and get into the supply. "Thanks to the blood for grades program, China now has enough blood for your transfusion. Unfortunately, the blood you got had untraceable levels of HIV and now you'll get sick and die, but you can do so knowing that some unrelated kid got into a better high school for your suffering."
That's not to say the U.S. doesn't have some of the same problems. The incentive to give can be strong.