Comment by tomp
The real answer:
If CloudFlare serves a lot of traffic (i.e. people on the internet are requesting stuff from CloudFlare's servers), they get better peering agreements (i.e. pay less) from internet network providers.
When "normal" people/companies connect to the internet, they're paying for the connection. Regional ISPs likewise pay Tier 1 network providers (i.e. "global internet backbone") for the connection, and are charged by bandwidth. When "popular" companies connect to the internet, they don't pay - e.g. a lot of ISPs would host Netflix servers for free (that way, they avoid having to pay for Netflix traffic to Tier 1 providers, but can serve it locally instead).
I can sort of intuitively see why that's the case, but any concrete or specific reasons on why "popular" companies don't pay?
The linked Wikipedia article doesn't really explain the reason behind it.