A:
I can only speculate that, as usual, it's about the money.
U.S. cellphone service providers seem to only grudgingly offer prepaid service. The phones that usually go with these services are low-end offerings... the providers apparently want to save the best phones for their locked-in contract service. And, they don't seem to want you to know about or have access to slightly-older but still-excellent phones that are also within reach of being purchased outright.
Best Buy isn't a cellphone service provider, but they do work with them. They put on display the standard prepaid phone options, and then have limited space for showing off the rest of the phones. So if the non-prepaid phones Verizon is pushing are the high-end, $600+ phones, instead of the numerous $200-$300 older models, well, that's what Best Buy will put on the floor.
Thankfully, we have the internet, where floor space isn't a concern, so Best Buy is able to offer the *exact* phone you want, provided you're willing to wait a little for shipment.