My theory is that for the major non-gaming companies- Google, Meta, and Amazon- building their own third party app store on iOS is not in their interest. They would essentially be carving out a ghetto for their own apps. Even if the law mandated Apple accept third party apps, Apple can still control that experience. And that experience will inherently involve friction. There will be friction to enable third party app stores. There will be friction to sign up for said stores, add payment information, and deal with yet another membership. Users would rather use mobile web sites before they have to jump through hurdles to install an app from a third party app store. There will be a public backlash against these companies for hoarding their apps in third party stores.

I think if they do introduce third party app stores, they won't take crucial apps- Google Maps, Facebook, Instagram, etc.- off of the Apple App Store. They stand to lose out too much by risking being dependent on their own new, untested third party app stores. And they would suffer a lot of heat from angry users for forcing them to sign up for and then manage yet another account.

Besides, these companies' apps aren't exactly the new hotness that inspire organic migration, unlike say TikTok. Imagine: users muddling through the Google Play Store for iOS® to get their Chrome, Google Maps, YouTube, and Gmail/G-Suite apps, and what else? The Google search app? The umpteenth Google instant messenger app? What would Amazon stand to benefit by duplicating their Kindle-oriented third party Android app store on iOS? Offer their Kindle reading app, the Amazon storefront app, and Audible? Does Zuckerberg really want to reenact the Facebook Home fiasco? Most of the time when these giants try to play in the others' home court, they tend to stumble pretty badly.

Gaming companies such as Epic, Valve, EA, UbiSoft, and now Microsoft-Acclaim-Blizzard might have a great chance at fostering third party app stores, given their unique content and gamers being accustomed to having to deal with multiple platforms with exclusive content. And er, a greater willingness to ignore user outcry over closed platform shenanigans.