They sell access to data (i.e., ads) - that is far more lucrative than selling the data itself. Only companies that are bad at tech just sell the data (credit card companies, retail, etc)

Cambridge Analytica was far more stupid - that was them just giving away data for free. Their old Facebook Apps APIs were wide open to collect whatever for free for anyone who would use your app (CA made those "do this fun quiz and invite your friends!" kind of FB games) and the APIs just said "we require you to delete this data when the user is done with the app" with no way to enforce it