Deeds and liens (ie. mortgage, home equity loan, etc) is public information. There are many companies that monitor public records and pounce soon as they detect a change.

While still very uncommon, there's a slight uptick in people buying property under the name of a corporation, trust, etc. Challenge there is keeping the officers / owners secret. Some states make it easy while others, likely including PA, don't. Regardless, it's a barrier.

Also, the government sells data too, such as the DMV (PennDOT). Doubt the spam calls are due to that. However, ads for insurance, etc could be. It's very difficult to hide one's personal information when so many are seeking to enrich themselves with it. Credit bureaus are another. It's endless.