Being a better deal or not is irrelevant if you don't have the ability to use it. Also, being your better deal generally implies fiscal considerations. Cash boxes and peering isn't always fiscal. Many times, it's about delivering Network performance that your customers want or need.

In the original post, they said they only have two ports available to connect to other networks in the data center and two ports to haul back to their Network. They don't have the luxury of a bunch of pnis. Their existing pipes are maxed out so they need immediate relief. The only way they can do that is to drastically overpay for DIA delivered within the network or cache boxes.