That's not illegal and monopolies are also not illegal in US, it is the anti-competitive behaviors that are illegal and these folks must convince the jury or judge that Apple intentionally blocked developers from competing against each other at their store. The laws do not prohibit owners from controlling their own stores, Apple has 100% ownership of their platform and are not obligated to open it up to anyone.
Unless the customers can prove that Apple does not permit developers from completing with each other, they're not going to win this one.
If they do, every single company in the US will be joining Apple on the appeal because it will break every company's rights to control their platforms.
Microsoft, Sony, Nintendo will be compel to open their platforms to alternative stores. Good luck with that.
Thank you Judge MikhailT.