Because end-users own their phones, and Apple restricting the ways software can be loaded onto the phone is robbing those users of their rights. The same applies to game consoles and other similarly locked-down devices.
If I buy a table, I can choose to stain it a different color, or put a tablecloth over it, or cut the legs off, or burn it for firewood. I have the right to use it however I want for whatever purpose I want, because I own it. For some insane reason bootlickers are willing to throw such rights out the window the moment you try to apply them to computer hardware and software.
Well the table manufacturer is not obliged to make it possible or easy for you to use the table as a chair, a bed or an airplane. I'm not really a fan of Apple but it's not that they are hiding the fact that you can only install software on the iPhone via the app store. It's the way they choose to design their product and it's an inherent feature of it (and part of their business model). Should all companies which build devices which include general purpose computers internally be legally obliged to make it possible (and easy) for users to install arbitrary software on them?
If I buy a table, I can choose to stain it a different color, or put a tablecloth over it, or cut the legs off, or burn it for firewood. I have the right to use it however I want for whatever purpose I want, because I own it. For some insane reason bootlickers are willing to throw such rights out the window the moment you try to apply them to computer hardware and software.