And customers aren't required to only shop at a single store. If the store doesn't have what I want, I should be able to go to another store.
Your Apple hardware is your Costco Membership Card. You aren’t able to buy Sam’s Club products using your Costco membership, and Costco’s under no expectation to make them available to you.
Your iPhone is not compatible with any software.
Some things are compatible and some things are not.
Edit: “Compatible” is not about the tech in this case (the binary would theoretically run) but about the terms of your agreement with the manufacturer.
If you buy a Costco fridge and with it a contract to only store Costco-sold food in it, then you have a better analogy. 80% of the world seems to prefer the AnyFood Fridge, and for some reason 20% buy the Costco with the agreement.
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Edit response: How many people do you think read the agreement they signed with Apple? How many realize Apple is increasing the price of software by ~30%?
You don't need to muddy the waters by making a ridiculous analogy that somehow equates a computer to a membership card (of all things!).
The computer is a computer. Full stop. There is a store on the computer. There should be other stores on the computer but they're not allowed because the people that make the computer are partaking in anti-competitive, anti-consumer shenanigans.