I'm not sure what you're talking about. Supporting HTTP/2.0 for my site was literally just adding the "http2" word to the listen directive of nginx. Since it's also used as a reverse proxy, the backend app server remained HTTP/1.1.
And you still notice the difference in site loading speed if your site has a lot of static assets.
How much traffic does your site serve? I'm not saying that turning the feature on is difficult. Anyone reading hacker news can go and configure their webserver to start serving this traffic....
but I can tell you that a site serving serious production loads (let's just say 100 qps)... nobody is just "flipping a config" and sending the protocol out the door.
And you still notice the difference in site loading speed if your site has a lot of static assets.