It's HW made by private corporation with their own SW and they can insist rules to make sure HW and SW systems are not abused so that most of the users get better user experience. They (Apple) are doing this to protect their users. If you don't agree with it don't buy their HW.

Can you install applications from third party providers on other app bases HW? such as Gaming (XBox, Playstation, Nintendo) Cars (Tesla, Benz, Nissan)

Or in non SW/HW world can you force stores such as Walmart, HomeDepot, Macys, Nordstorm to sell goods from third party seller? And, even these stores charge fees for selling items made by other manufacturers.

If you don't like ecosystems made by Google and Apple don't buy their HW/SW.