You act like companies wouldn't produce viable alternatives given the opportunity... and you act like Steam isn't better because of the competition.
Apple is putting forced restrictions on their platform because they want to squeeze everyone who comes through their doors. Apple acts like they are the only ones who can create a "brand, real-estate, parking lots, etc" when in reality, it can be done a lot better by any number of other companies - the only reason they can charge 30% is because of artificial restrictions put in place so... they can charge 30%.
Walmart doesn't want Target next door... because then they'll have to actually innovate to keep their customers.