There are numerous large data brokers that take in all the consumer data they can buy or obtain through governmental sources. This includes credit data, car registrations, purchase histories through things like affinity cards, data shared by membership organizations, ad networks, etc. If the data can be had, they'll have it.

Once they have the data, then they process it to extract greater knowledge. This allows them to deanonymize data and be able to attribute it to individuals.

If you are leaving a record in a database anywhere, you can reasonably assume that data is included in this, and that "psuedoanonymizing" it doesn't really protect you much.