> Every one of those platforms tightly controls access to their platforms.

They actually can't. Not legally, anyway.

I am not a lawyer, but Nintendo famously lost a lawsuit, when attempting to block third-party software distribution : https://openjurist.org/16/f3d/1032/nintendo-of-america-inc-v... Sega (back when Sega was a major console competitor) also lost a similar lawsuit, when attempting to block third-party software distribution : https://openjurist.org/977/f2d/1510/sega-enterprises-ltd-v-a...

If we still had anti-trust enforcement, this should set precedent against what Apple is doing here today. We already decided this issue in the 80s and 90s, making a specialized locked-down computer (i.e., a "game console") does not entitle you to own the entire software market for that device. And so long as you don't steal copyrighted materials to do so (see Nintendo v Atari), you are allowed to reverse engineer and sell your own software for these devices, without any royalties or licensing owed.

If you want iPhones to be treated like "gaming consoles" instead of computers, then it is already legal to jailbreak an iPhone, distribute your own apps (or entire app store) and sell to iPhone users, without ever paying Apple a single penny.

It's even legal by precedent to modify other people's software when selling your own third-party software (see Game Genie / GameShark lawsuit, it's legal to sell a program that modifies someone elses copywritten software, so long as you don't include or redistribute the original copywritten code).

...and if all car manufacturers bought engines from the same factory (TSMC), used the same satnav (except one brand, who had a slightly-worse in-house clone), and an accelerator and gearbox from exactly one source (Google search) would you be more concerned about anticompetitive behavior? What if the manufacturers were allowed to produce "accessories" like batteries, tires, and child seats that refused to work in any other car, and actively sued repair shops that weren't official dealerships?

Apple and Google may be competitors, strictly speaking, but the reality is they've pretty well carved up the market between premium buyers mostly concerned with fit+finish, prestige, and compatibility with other Apple devices, and the operating system and network infrastructure for, well, everything else.

It's absolutely a duopoly, and so minimally competitive: either Google or Apple would happily claim leadership status, but neither party really wants the other to go away lest actual competition or government intervention cause them to lose control of their patch of ground.

There is no competition, because there are exactly two viable platforms for mobile apps. All the others are footnotes.

> "Which competitors to $car_manufacturer engines are there for $car_manufacturer cars?"

Interesting and rather unfortunate that you should use that example, since the landmark Magnuson-Moss Warranty Act famously invalidated automakers attempts to revoke their products' warranty if aftermarket parts were installed. It's a clear example of a consumer-hostile practice that was deemed to be unfair and regulated, even though no monopoly was involved.