Apple, on the other hand shares the market with Android. Globally it's a minority share. Yes, in the US, Apple has a bigger market share than it has globally, but Android is a real competitor even there. So I'd suggest the two situations are quite different.
If it's not a monopoly (which would be fine by itself anyway), it's hard to make the case that they are leveraging that monopoly in unhallowed ways.
All that said, clearly the DOJ think they have a case, and I imagine they've spent a LOT of man-hours thinking about it and forming an argument. More than the no-time-at-all I've spent thinking about it.