That’s more likely to be the answer. If Apple were content having Google’s sloppy seconds while having full opportunity to make Alphabet level profits¹ then the world would turn upside down. It’s more likely that Apple doesn’t see an easy avenue to those mountains of ad-revenue money without compromising their privacy image. Might as well take Google’s cheque to the bank the same time as iCloud subscription profits cheque.

*1: I should probably clarify that I mean on top of what they already earn.

Literally one of the bullet points:

In order to create a “viable” search engine business, Apple would be required to “sell targeted advertising,” which is “not a core business” for the company and would go against its “longstanding privacy commitments.”