Say what?? I’ve also worked in the ad industry and deanonymized personal data is shared and sold routinely. You speak of statistics and large segments but every advertiser I’ve interacted with is either doing individual-level targeting or striving towards it.
Only if they're clueless.
For example: Nike really wants a dataset of "people who buy expensive sneakers for fashion purposes".
This dataset is probably hundreds of millions of anonymous people, and not personal data. If there was a way to get this dataset directly, Nike would do that in a heartbeat.
Unfortunately, as of 2019 the only way to get something like this today is by, e.g., crossreferencing credit card purchase info with Twitter browsing logs, which leaks a shitload of sensitive private data.
For ad purposes personal data collection is a bug, not a feature.
I’m not necessarily talking about demographics, but rather clickstream data, and anything categorical that you can get your hands on. You join that to your CRM and build a model to predict buyers. A really good predictive dataset for marketing purposes is simply a list of time stamps and names of visited domains. With the right feature engineering, that becomes an excellent proxy for demographic data, current buying appetite, and a whole lot more.
At the end of the day, you don’t even necessarily need to know what the data means as long as it’s predictive. And there are plenty of brokers out there who will let you test their data for free with an agreement to pay if you end up using it at scale. All of this revolves on using PII for matching.
I’m sure what you’re saying is true for some marketers, but there are billions being made on PII keyed data.
Let me repeat again. PII is a crutch used for matching, because current matching/segmenting technologies are crude.
Advertisers don't want PII. What they want is target audiences with predictive power, which means data sets where the central limit theorem holds sway. (I.e., thousands and millions of people lumped together.)
If advertisers could get at these segments directly without PII, they'd do it in a second.