> They are actively and publicly fighting against my (their customer) interests.
If Apple allowed unrestricted sideloading or third-party app stores, then it loses its leverage to hold apps accountable to any guidelines.
A few major players would switch to using the alternative method (eg Amazon would want to sell digital items and use its own payment system), legitimizing it, and then everyone who wants to ignore the guidelines for less admirable reasons would follow suit.
Less technically savvy users would follow the prompts to install an app with extremely mixed results. And once there's no one way to install apps, it makes it that much harder for them to tell if an app is legitimate or not.
That's maybe fine for more technical users, but for people who just want to use their phone as an appliance rather than verify the chain of trust for an app, there's no discernible benefit. The time required to verify an app is non-negligible, and the risk is pretty much infinite with respect to what information they give it.
And sometimes you don't really have a choice whether to use an app or not. Your employer or locale may make or imply decisions on service providers for you, and the reason for choosing those service providers likely has nothing to do with how their app treats end users. They won't need to clear any quality bar to offer an app at all, and a locked-in customer has less negotiating power than Apple.
Apple has positioned itself as a premium product which is going to make things simpler (ie reducing executive overhead) by making decisions for you. Saying "no" to features to keep things focused for the largest group of users is hard, and those decisions are going to trend towards the largest demographic using the platform, which is probably less-technical users who don't hang out on HN. If you want to customize the platform, then that's Android's competitive edge.
You can even sideload apps with a developer license - that's essentially how UTM is installed: https://docs.getutm.app/installation/ios/
While that does mean you have to put down more $$, it also effectively narrows the people sideloading apps to people who "know what they're doing" (or at least have demonstrated a higher bar of tech-savviness and clicked through more legal waivers)
What do you want to do now that you can't do with the current state of affairs?