Thats not remotely true. ESNI is a draft IETF spec - https://datatracker.ietf.org/doc/draft-ietf-tls-esni/. It just so happens, that right now CloudFlare and Firefox are the ones that implement it. But any particular feature, regardless of how great it is or how well specified by a standards body, must have a first implementation by someone. And it's really not that shocking that a group like CloudFlare wants to be at the forefront of new web technologies AND also has the resources to pay for it. What does boggle the mind that is that everyone freaks out when a draft IETF standard is implemented. What do people want? For it to spring into existence fully formed implemented by all browsers, operating systems, DNS software and providers, etc all that once? That would be ridiculous - and worse, if there aren't a few experimental implementations to work out the issues, even if that could happen, what would be implemented would probably have significant issues that we'd then be stuck with forever.
This isn't a Cloudflare-specific feature. It's an IETF draft standard: https://tools.ietf.org/html/draft-rescorla-tls-esni-00 Just as we've done with other standards in progress (QUIC, TLS 1.3) we've implemented on our network. That helps get the standard tested and adopted quickly. Literally, anyone can implement that standard, there's nothing "Cloudflare" about it.