Because they have the choice of letting you choose what happens with your personal data (if you live in the EU) or not doing business there at all. In other wo

Because they have the choice of letting you choose what happens with your personal data (if you live in the EU) or not doing business there at all. In other words, if there's even a chance that you say no to them (ab)using your data any which way they like, they consider you a net negative to their business.