Should all those sites not benefit from the speed improvements that HTTP/2 offers? It seems unusual to couple HTTP/2 with TLS, again, it's not the spec that does this but the vendors who are doing this.
The bigwigs of the industry will throw tons of developer resources at converting everything to TLS (haven't they already for the most part?) and then deploying HTTP/2. They already throw tons of money at being the fastest out there.
I find it interesting (worrying?) that while a spec does not specifically enforce a requirement, large browser vendors have enforced it and created an imperative for pretty much everyone to comply if they want the benefits of the new protocol.