They don't do it out of goodness of their hearts, which is why it's more solid than relying on goodwill - Microsoft simply has an offering that depends on that for certain high profile clients.
Which makes a lot of sense, because you couldn't run Windows on a Mac nor MacOS on PCs from the likes of Dell or IBM, and you couldn't run third party software for Macs on Windows or vice versa. By contrast, you could run various types of Unix on a Dell, and run Windows software on OS/2 or DOS software on DOS competitors other than MS-DOS.
That distinction seems like it might be relevant to the current situation.
It remains objectively inarguable that Apple does not have a platform monopoly on (ARM-compatible) smartphones the way Microsoft did on ("Intel-compatible") PCs.
If you have a car that runs on diesel fuel and there is only one company that sells diesel fuel, it seems like you want to claim that it's irrelevant and isn't a monopoly because there is another company of the same size that sells gasoline. Is it not relevant that you can't actually use that in your car?
People should be free to use other browsers and accept higher power usage, or "privacy risk" without Apple forcing their own browser engine, which limits functionality of all web browsers on iOS.
What Microsoft did by bundling IE with windows was far less egregious. Could you imagine if Microsoft forced all browsers on Windows to use IE as a webview? Holly shit people would be rightly pissed.
Apple does this specifically to prevent competition from web applications so that developers have to use Apple's app store, where Apple can charge the developer/customer money. It's spelled out in the DOJ lawsuit against Apple.
https://www.justice.gov/archives/opa/media/1344546/dl?inline