You, and the NTSB, are in agreement on this. However, the airlines would like to make money, and kicking off 5 people yesterday in San Diego would not have made anyone happy.
Money. That's how the whole "lap child" thing got started way back when. The airlines wanted to encourage businessmen to take their wives on trips with them (selling more seats), but knew they'd have a better chance of that happening if the baby could come along for free. At the time, babies rode on Mommy's lap in the car, too, this was long before automobile carseats. Thus was born the concept of "lap children". Now pax are so conditioned to expecting free travel for babies that it'll be a really, really hard time to change that rule.