"Not all of it" is doing a lot of work. It's estimated that Apple ad revenue will be ~2-3% of total revenue in 2024.

Sorry, i didn't mean to be disingenuous. i meant, ads are not the main source of its income.

And in this context, that's why it is not a foolish choice to spend money on something that it's hard to sell ads on as long as it helps sell more iPhones.