Isn't everything harder at scale? That's not a barrier for entry though.
for a global cdn... it quite literally is
Point taken, For a Global CDN - scale is the point of entry.
Building a CDN absolutely is hard to do at scale.
You can't build a Cloudflare competitor in AWS/Azure/Linode/DO/etc. You need your own data centers. Multiple of them across the country, ideally around the world if you want to serve the whole world.