I think the main thing to grapple with is the idea that even laypeople who aren't security or SWE experts may want to protect against the highest risk profile possible, even if they don't personally understand what they're giving up. (And, for most of these people, I imagine they're giving up a freedom they might not have ever thought of using in the first place)
Strawman but, If you want to make a device called "securePhone 2027", where not even an evil maid attacker (say, a national security agency who has spied on you over your shoulder for 180 days and has thus seen all of your passwords) can install spyware on your phone, what sort of qualifications do you need to have in order to purchase (or qualifications for a manufacturer to sell) such device?
Part of the issue in arguments like this is in saying that, because the iPhone is the most popular phone in the United States, they should be forced to compromise on security because enough buyers aren't aware of the compromises they're making in order to have the iPhone. So if you still want companies to be able to sell a brick that never runs unsanctioned7 code, you either need
(A) setting an upper bounds (market share?) to how big a company can get before they must compromise on security and allow people to self-compromise via going through multiple hoops to disable security protections (e.g. disabling SIP on a Mac). (B) means-testing that the customer understands that what they're buying could compromise their security (C) some key ceremony for allowing said device to be unlocked. I imagine a 1 month waiting period plus needing to show passport and proof-of-non-coercion across multiple nation-states could work? maybe only if they're not apart of a shared intelligence network coallition (like five/nine/fourteen eyes)?
The fact that the iPhone is incredibly resistant to all forms of widespread malware is really good for society at large. Like, the only known widespread malware (outside of web-based scams calling Alert("Apple has compromised your device, call this number")) has been developer-distributed malware due to chinese developers releasing apps via a malicious unsigned Xcode app [0].
Just like PKI infrastructure, vendors could embed and tie into a TPM similar key infrastructure that would be the only part you couldn't touch (key storage + key validation and signing implementation so it can't be tampered with). I mean, even there the code could be open and only the key material would be secret.
(I find revocation a harder problem, really)