Developers have come to the same conclusion, it's to their benefit for the customers to all be on one store with one set of policies and features so that's where the majority of the apps go.
So what are you going to do, force Apple to become a fragmented Android copy with multiple stores and side loading that a tiny fraction of techies actually use? Those people already have that on Android if they want it. Honestly you'd just screw over Apple and a few other people over a principle hardly anybody actually cares about or benefits from. It certainly wouldn't make any significant commercial difference. We ran that experiment and the results are in.
The idea that users would all be side loading apps and developers would be making far more money having their apps spread across 5+ different stores that would compete down to lower prices is delusional. If that were the case, why has this not happened on Windows or MacOS where side loading is actually the default yet Steam, GOG, etc still charge 30%? It's crystal clear that's just the split the market has converged on through a competitive process. After all Steam has competed from day one with a default split of nothing for direct downloads from the software publisher but has thrived charging 30%. If that's not direct market validation I don't know what is.