Utility regulation only works when the product doesn’t change and is a fungible commodity - power is power. It also is about driving prices down for consumers for that commodity.
The iOS and Google platforms have barely existed more than a decade, and the platforms are constantly evolving. New platforms and ecosystems are emerging too, with Facebook/Oculus, Valve/Steam, Amazon with Fire/Alexa, etc.
Enshrining today’s dominant app platforms as the government sanctioned ones will surely stifle their evolution and innovation, because that’s what declaring something a utility is: a commodity with no differentiation.
The crux of this matter is that end consumers generally do not care about the 30% cut, It’s a retail cut they’re used to from other platforms like Sony PlayStation, or Ticketmaster for concert tickets. it barely impacts them (and arguably the curated stores are a better overall experience). I also don’t think almost any consumer of iOS would agree their App ecosystem experience is fungible with Android or anyone else. This is entirely driven by Devs and publishers that want better margins.