If they created the market, why is this a problem? In my head, it’s their market, so they can decide what to allow and provide, the same way Kirkland does at Co

If they created the market, why is this a problem? In my head, it’s their market, so they can decide what to allow and provide, the same way Kirkland does at Costco. They’re not even a majority, let alone a monopoly. It’s anti competitive, but I don’t understand the need for outside intervention.