Search advertising doesn't require massive data collection, just bidding on search terms. Anyways, I bet anything Apple makes on app store ads is a rounding error compared to their hardware business. They probably don't care that much, and certainly have no need to go into the surveillance business.

They have audience options for ads (like age/gender/location, see http://searchads.apple.com/how-it-works/#features), meaning they collect data about their users as well.

Also, they colluded with other companies to, effectively, keep employees' wages down. Amount of money they saved was probably a rounding error for them in this case too.