They can't because smartphones are almost entirely closed to this idea and that's the most important device for consumer adoption. Although Android is slightly more open there are, after ~17 years, zero mainstream Play Store alternatives or mainstream popular sideloaded apps in most countries, while iPhone is entirely closed to this in the vast majority of countries.

Best they could do is have each app individually submitted to these stores or streamed, either way they need to use the platform in-app purchases mechanism and on Google Play I believe they have to pay a large fee on third party payments, while Apple prepares their Supreme Court arguments that they should have an even larger one.