The point is that more, different, better and cheaper options might exist. The fact that people are still willing to trade in a large captured market does not mean that competition is not greatly distorted in favor of the market's owner.
> The point is that more, different, better and cheaper options might exist.
They can, on Android, which worldwide is about 75% of the market.
> competition is not greatly distorted in favor of the market's owner
If Apple were primarily engaged in making its own apps that compete with apps in its marketplace, then yes, that is distorting the competition (and one could argue that it does this with certain apps like Mail). But the fact that it takes a cut from anyone who wants access to its user base, doesn't stifle competition per se.
This is primarily about access. If I want to set up a popup store inside a fancy country club to access a captive market, I'm going to pay a lot more in fees to the country club than I would if I put it up in some random strip mall. This is no different.