For starters, nobody forces you to sell merchandise for this particular team's fans...

But the analogy breaks down here, because merchandize such as t-shirts is not dependent on the stadium to be used. You could sell it outside the stadium.

Whereas iOS software leverages the fact that the iOS is being sold, maintained, having the necessary APIs, and so on, and that iOS devices are being made and sell decently and lure people willing to pay for apps.

So it's like you want to sell a ware that's inherently dependent on the stadium (hence my stall analogy), but you don't like the terms of the stadium builder/owner/maintainer that allows businessmen to have those stalls on their stadium...