Surveillance capitalism refers to the practice of monetizing data collected about the users of a service. Doing so increases the incentives for collecting more user data, which in turn violates user privacy further.
The practice may be legal, if the user consents to the collection of data. Some businesses offer free services in exchange for the use of user data. Unfortunately, it is not always made sufficiently clear how the data is used, and whether it involves the collection of personally identifiable information.