The entire business model of Facebook is to collect as much data about you as possible, to data mine that data to make hypotheses about you and your interests, and then sell that to third parties, thereby passing your personal information on to a larger audience.
Facebook knew for two years that a data firm harvested data from more than 50 million profiles of U.S. voters without their permission but did nothing to protect its users, Guardian reporter Carole Cadwalladr told CBSN on Saturday. Cadwalladr said Facebook threatened to sue in a bid to prevent The Guardian publishing an exposé on the data harvesting.
Source: Facebook knew of Cambridge Analytica user profile harvesting for 2 years, never acted – CBS News
This occurred by design of Facebook:
“It worked because Facebook has built the craziest most invasive advertising model in the history of the world and someone took advantage of it.”