I can tell you from first hand experience their data trove isn't the most valuable for farming out for AdTech. They take in a lot of opt-in telemetry and bend over backwards to anonymize it. There's also very clear demarcation of PII and if you even work around something considered PII you as an engineer need to sign all sorts of extra paperwork.

Even if any individual manager or director decided they wanted to leverage PII they'd quickly run afoul of Apple's extremely legally conservative legal department. Because of this data is sanitized and anonymized before it's collected and then further after it's collected.