The data is only useful in aggregate, but different people/use cases require different types of aggregations. Using pre-aggregated data is difficult, because it almost certainly hasn't been aggregated in the way that's convenient for whatever analysis you're trying to do with it.
The aggregate data is often more useful in commercial use cases, but plenty of use cases need the indivual data as well.
Private investigators, three letter agencies, and any company wanting to send mailers to my new address when I move all need the individual data to target me specifically.
I totally agree the aggregate data is given more value in a commercial market heavily focused on advertising and now training LLMs, my only point was that there are markets that highly value individual data as well.
Sure, it is fractionally "valuable" in the sense that it is worth some tiny percentage of the large datasets it belongs to that get purchased for significant amounts.
I think the point stands that it wouldn't be easy to sell your individual data, and even if you could, it would be for a pittance from someone who is looking to build a large dataset. They certainly wouldn't be giving you an amount that justifies advice like "hold on to your data".
