"I guess they don't trust their caches at the network edge to deliver their service?"
Check some of the public stats for ISP's using Netflix CDN's (i.e. XMission - https://stats.xmission.com/public/bandwidth/) to see the difference in user traffic versus traffic sent to the Internet.
This is to protect under-provisioned exchanges (i.e. either rural locations with a lack of bandwidth or urban sites on the pending upgrade list) and mobile
Biting the hand that feeds IT
