CDNs are expensive to build, and often not very useful to customers until you've built out a large portion of it (actual hardware required, you can't just run it atop AWS). On top of this, much of the money is in Enterprise. So you've got to compete with Akamai, AWS, Fastly, Incapsula, Cloudflare, and several other notable ones to get any customers to speak of.
There are smaller CDNs out there. You can find them readily enough.
Depending on how you integrated it and how deeply, it may be trivial. Certainly going from one DNS-based CDN to another can be pretty easy - a Cloudflare / CloudFront swap could be quick.
Which suggests to me that CDNs are already a commodity in some ways.
There are smaller CDNs out there. You can find them readily enough.