This was true for a huge number of newspapers - user data was an enormous part of the ad business in the print days as well, and has some striking similarities

This was true for a huge number of newspapers - user data was an enormous part of the ad business in the print days as well, and has some striking similarities to what happens today online. Back then it took the form of the subscriber database as you suggest, and was used to help target and sell ads in the paper. The print industry often "sold" the subscriber list in detail to prospective advertisers to demonstrate the potential reach. Losing detailed subscriber data was one of the primary objections many papers expressed to Apple's app store distribution model which can effectively render readers anonymous, as this was apparently one of the most valuable things they had.