You can’t run services in lets say GCP and expect to save costs by outsourcing the data to some cheap providers. They all have additional bandwith fees in place to lock you up into their ecosystem.
We do have at least one customer that is using us as their primary CDN. I looked up their invoice just to understand if that is some kind of ongoing abuse but no they are doing that since a few months now. About 1 PB of download traffic for 7000 USD and just a few hundert USD in storage fees. So much on the theory it works for only storage…