What other way is there? Waiting, until they do it out of pity?
The EU was playing around with the idea already, they just went a little overboard in their first drafts of the Digital Markets Act. But I think we'll see something like that come out of Europe soon.
Did we legally force browser vendors to support web protocols and standards? Didn't the market solve this for us — i.e. if you created a browser that didn't do http, or https, or web sockets, or support a video or an audio html tag, then it would just die, because people won't use it. Are we admitting here that interoperability does not bring any competitive advantage, and that you need a state regulator to force you to do it?
Did you not pay attention? Microsoft tried exactly that, for close to a decade. The only thing saving the ecosystem was their own incompetence at developing an at least half decent browser.
Now Google is trying the exact same trick, and unfortunately, they are doing much better. And the thing that's probably going to thwart their efforts is not the open market, but the closed market of Apples "absolutely-nothing-but-Webkit" walled garden.