The relevant reasoning [of how this makes sense in terms of alternative to privacy and regarding GDPR compliance]:

The option for people to purchase a subscription for no ads balances the requirements of European regulators while giving users choice and allowing Meta to continue serving all people in the EU, EEA and Switzerland. In its ruling, the CJEU expressly recognised that a subscription model, like the one we are announcing, is a valid form of consent for an ads funded service.