Most of those sorts of companies (both B2C and B2B) ultimately end up selling the user transaction data (or some derivative analytics thereof) to hedge funds. It's used (for example) to forecast the revenue of B2C companies in advance of equity earnings announcements.

NB: I don't have an issue with user data being mined for things like market research if it's a situation where the product is free and users can be easily made aware of it. But I find it dishonest if the company mining that data is doing so without direct user consent, or in a "backdoored" manner using their status as a downstream client's "affiliate" for T&C purposes.