First, privacy policies are mandatory and are always a bit frightening to read, because most users are still in denial that the beloved service they are using is actually re-using their content and details for money making purposes.
However, truth is that there is a demand for statistics based on so called "big data" and data for direct advertising.

You can get an answer to your question simply by reading the policy. It states the reasons for sharing your data. One of these reasons is for advertising purposes. Other reasons are e.g. the ability to contact someone when there is an emergency or for legal purposes.

If you live in the EU you are in your right to request a full copy of all the personal data acquired by the service you are using.