If browsers had a "provide us some preferences to customize advertising" flow in their onboarding, users would feel in control, and the data might be of high quality. Ideally, you'd have some compartmentalization options (don't show community X my interest in product Y). That's completely infeasible now: there's such a hostility and adversarial relationship with customers, that any data provided through a voluntary, opt-in process would be seen as suspect from day 1. Not without reason-- users would be prone to select garbage in the attempt to reduce ad load or cause undue cost to advertisers. Even if the users played along, would also likely be hijacked by self-serving technology players-- would there be an interoperable way to probe customer preferences, or would they be aggregated by, and only available on, specific platforms?

Since the industry has already destroyed any trust and quality relationship between users and advertisers, AdTech has to resort to continuing to poison the ecosystem through constant surveilance to retrieve "more reliable" data than asking customers what ads they might care about.

There's a potential to claim some subtext in user activity that would reveal preferences the customers won't manually disclose, but that's also the exact that the surveilance practices cross from useful to creepy.