I don't know what "need" means in this context. That is what they do - sell your data. Perhaps a different company that didn't do that could exist, and in a different sense, CK doesn't "need" to do anything, even exist. But they do exist, and do sell your data.
"Need" means they make money without selling data directly (as described above). In fact, they probably do/would make more money through direct conversions than data sales when the data is generally available anyway.
In other words, they have access to data that is available to anyone who can make a soft inquiry. That's a lot of people. It's easy and cheap.
