It's more a portfolio of companies that many make less, but a few hits cover the investment in the rest (the standard publishing and tech investing story). If the hits are going to take a 18% rev loss compared to say Epic's 12% store, then that's 18% less funding for the rest if things are invested efficiently/predicted well for the portfolio.
There is a huge difference between making a “service” exposed by an app and making an app.
How many successful “apps” do you know of? And most successful “services” that people access through the App Store don’t go through the App Store for payments