What other company could have done this? Was the fact that Google controls so much of the entire usage chain (chrome, google.com, youtube.com) irrelevant?
In this specific case only three other companies make web browsers with significant market share (Mozilla, Apple, Microsoft), so I guess you could argue only those three companies could have done this particular thing and you're correct that only Google owns Youtube.
But more generally companies have written up IETF paperwork for other protocols. Lots of Microsoft protocols have RFCs for example. But one thing that's less common is actually engaging with full-blown IETF working group standards development like Google did here, as opposed to just saying "Look here's the protocol we built, you can use that, or not". The IETF is totally happy to accept what I guess you could call a "donation" of that sort, and it's much less effort. Maybe you take some internal documents, you reassemble them into the rough shape of an RFC, you publish that draft, you get a bunch of feedback about that document, focused on clarifying the explanation, making sure you cover everything required, and so on rather than altering the protocol (which you've maybe already actually shipped in a product) and after maybe 6-12 months you've got a polished RFC ready to publish.
If you use a work VPN for example, or a corporate WiFi network that's not just a few home WiFi routers with a more professional SSID and password, you probably end up using protocols Microsoft "donated" in this way, like PEAPv0/EAP-MSCHAPv2 - these protocols are awful but there was no multi-step process where other vendors improve on it and then they eventually reach consensus and publish. Microsoft shipped products that do MSCHAPv1, then wrote it up so that other products could interoperate with Windows, and when they made MSCHAPv2 they followed the same path.
It might have worked if the majority of web servers had been Microsoft’s, but my recollection is they never got close to having the majority of the web server market.
The crown went from NCSA to Apache and then only recently to Nginx.
But more generally companies have written up IETF paperwork for other protocols. Lots of Microsoft protocols have RFCs for example. But one thing that's less common is actually engaging with full-blown IETF working group standards development like Google did here, as opposed to just saying "Look here's the protocol we built, you can use that, or not". The IETF is totally happy to accept what I guess you could call a "donation" of that sort, and it's much less effort. Maybe you take some internal documents, you reassemble them into the rough shape of an RFC, you publish that draft, you get a bunch of feedback about that document, focused on clarifying the explanation, making sure you cover everything required, and so on rather than altering the protocol (which you've maybe already actually shipped in a product) and after maybe 6-12 months you've got a polished RFC ready to publish.
If you use a work VPN for example, or a corporate WiFi network that's not just a few home WiFi routers with a more professional SSID and password, you probably end up using protocols Microsoft "donated" in this way, like PEAPv0/EAP-MSCHAPv2 - these protocols are awful but there was no multi-step process where other vendors improve on it and then they eventually reach consensus and publish. Microsoft shipped products that do MSCHAPv1, then wrote it up so that other products could interoperate with Windows, and when they made MSCHAPv2 they followed the same path.