I think that for most people, especially new moms, it is just expected that you keep them in the infant seat at all times. I don't know if you have noticed or not but they aren't eve referred to as "car seats" anymore, they are "infant seats" (http://www.cpsafety.com/articles/infantshop.aspx
) or even "infant carriers" (http://www.theaa.com/motoring_advice...s_infant.html)
. With the heavy marketing of travel systems, it is no wonder that so many people have bought into this marketing ploy that is designed to keep kids in the car seats for as long as possible. It doesn't matter that a baby who falls asleep in an infant car seat will continue sleeping if taken out of a car seat and put in a sling, or even a stroller, or even held, it is the fact that 95% of what is seen in public is babies confined to infant car seats while not in a car.
It's the same as people who live in a formula bottle-feeding culture, if they aren't exposed to alternatives and only one method is very heavily marketed to them, you can harldy blame someone for following societal's norms and buying into what is being sold them.