This is common for any company that operates a CDN. It just so happens Netflix is a big enough content deliverer that they run their own network rather than pay to use someone else’s.

I was involved in starting a streaming service in SE Asia and the costs of 3rd party edge caching (Akamai etc) were significant. So much so that it made the business model non-viable without work arounds. Eventually we partnered with ISPs and piggybacked their edge caches.