I certainly don't fit the bill of a shrewd, price-conscious buyer. However, I have read on HoFo, don't know if it's accurate or not, that there is a pecking order of priority for broadband access. Postpaid is higher on that list than prepaid. The list includes those who haven't reached their various limits, those who have, proprietary prepaid, third party prepaid, etc.
If one were in an area of congestion and needed top priority, that may be one reason for opting for the more expensive postpaid. Just guessing.
Also, I've read where some features are available on postpaid which are not on prepaid. Probably most would be better off on prepaid, if they can afford to buy their phones some other way than postpaid.
There seems to be a lot of people who are happy with Visible, which is a Verizon unlimited prepaid plan for $40 per month. By joining a group, you can get it down to $25 per month.
Visible | The Future Of Phone Service.