Why are the HTTP/2 is only enabled by default?
HTTP/2 is based on SPDY and is the second major revision of the Hypertext Transfer Protocol, the application protocol for the Word Wide Web. SPDY is an open networking protocol developed primarily at Google. SPDY also for transporting web content. In addition, it is help to make the web pages loading faster and reduce latency.
However, SPDY is enabled by default for all customers that using the SSL on their site through Cloudflare.
After that , HTTP/2 is only enabled by default for Free and Pro plan customers. Therefore, for all other customers must be allow under the “Network” request.
Please refer to the following article to know more.
Knowledge Base: Can I disable the HTTP/2 for my website?