This is wrong. There are plenty of ads outside of the App Store, like:
- There are adds for iCloud in the Settings app.
- There are ads for Apple News in the Stocks app.
- There are adds for iCloud in the Settings app.
- There are ads for Apple News in the Stocks app.
But.. I’ll grant the second - there are ads for Apple News in the stocks app.
So no. There are not “plenty of ads” outside the App Store.