The morality and/or ethics of the situation aside, I've still never gotten a satisfactory answer for why we should care that the iOS ecosystem is a walled garden to the point of wanting the US government to step in, but not maintain the same energy for the PlayStation, Xbox, Switch, etc ecosystems.

I know that the deep down answer is that many of the people in these discussions think gaming is frivolous. But my PS4 is objectively far, far more powerful than any phone I've ever had, and comes with a selection of applications beyond just games - a web browser, photo/video editor, music and video streaming, a social messaging system (and social network, via the third-party Twitch). And going by hardware alone, it would be capable of much more than that if only it wasn't so prohibitively expensive to develop for.

How is that so different from what the vast majority of people use their phones for? Yet people are far more up in arms about the $100 yearly fee for the Apple Developer Program than about the thousands of dollars ($2500 for a dev kit) it costs to even build and run a game on the PS4 (plus you have to be a registered company).

Why should an iPhone be treated as an open, general-purpose computing device if a PlayStation is not? Why should Apple be forced to make it one?

I personally think the question is reversed. Now that the consoles are rather clearly general purpose computing devices, why are they not asked to be open?

The two arguments I have seen seems pretty weak to me: they are not general-purpose computing device and that's how they make money. I think you debunk the former pretty well, and as for the latter they are not entitled to a specific business model.

There is a third argument which is admittedly not weak: the extremely high walls are a large part of how their measures against cheating remain miles ahead of what games on PC can offer, which is invaluable to both developers and players (especially for multiplayer games). There's tons of data to back that up, but as just one point the recently-released Fall Guys was plagued by hackers on PC from pretty much day one while there hasn't been so much as a single report of a hacker in the PlayStation version of the game.

Even then, I'd be okay with Sony offering an "unlocked" version of the PS4 that's blocked from accessing the PlayStation Network; modding offline, single-player games is not cheating in any real sense of the word, and then at least more hobbyists could develop and run things on it without committing to becoming capital-G Game Devs (or being game devs at all - there's plenty of space for regular apps as well).

At the very least, they should allow (easily) unlocking the bootloader and installing a different OS, even if it would mean that that particular console can never install Orbis OS (which funnily enough is based on FreeBSD) again. It frustrates me to no end that my PS4 will become effectively useless to me if I purchase a PS5, when it would make a perfectly good desktop with a wipe and a Linux install (some people have managed to hack this on older firmware).

That actually mirrors my stance on Apple - I have no problem with iOS as it exists, but I do have a problem with not having any other easy OS option on iDevices.

Imagine if your builder tried to control what appliances you were allowed to install in exchange for a cut. Digital restrictions to define a market defined not by technical limitations but by arbitrary restrictions designed to extract a cut of the profit is relatively new in the grand scheme of things and its a bad road to go down.