There is also the possibility that without a [paid] curator (the vendor, like Google or Apple) we can't have security for how do we ascertain provenance? You might not buy that argument, but the vendor will make it, and it will resonate with the public and/or the politicians.

Establishing trust with hardware, firmware, and operating system software is currently an intractable problem. Besides the halting problem and the reflections on trusting trust problem (i.e., supply chain problems) the sheer size of these codebases and object code (since you'll need to confirm that the object code is not altered as in the reflections on trusting trust paper) is just too big for the public to be able to understand it. Sure, maybe we could use AI to review all of this, but... that's expensive if every person has to do it, and... that's got a bootstrapping problem.

Basically the walled garden is unlikely to go away anytime soon. It would be easier to change the rules politically to do things like reduce transaction fees, but truly allowing the wide public to run anything they want seems difficult not just politically but technically, because the technical problems will lead to political ones.