In a prerecorded video CDN managing that catalog is a PITA and does drive meaningful infrastructure cost. You need the "right" content to be in the correct location for low cost peering/transit/distribution, on the correct media for the total throughput:size, in the optimal number of encodings for efficient/quality playback, etc. This job is a lot easier when the provider controls the catalog, and has a limited catalog size. See some of the OpenConnect talks where they're "preloading" content offpeak to optimize IO allocation on the appliances. It was an absolute nightmare to try and manage with a many PB catalog with 3P content that service didnt control the release/popularity of.
Edit: source, principal at AWS and was responsible for a lot of the prime video delivery once upon a time.