As explained in the link it’s mostly because the judge in that case decided that the relevant market was “mobile game payments”, which immediately invalidated the monopoly claim, because “Apple doesn’t have a monopoly in mobile gaming”.
It will be very interesting to hear Epic’s arguments tomorrow.
I personally think Google Play’s model should change so that app developers pay either an upfront sum or a flat monthly rate to have their apps listed if they include in-app purchases (because hosting costs money and Google needs a viable business model for its app store), and obviously have their apps listed for free if they don’t have in-app purchases. That would be a bit fairer IMO. The way Google tries to get away with a Unity-style tax to siphon the proceeds from an app’s success is just wrong.