What does Facebook offer for all that money that is necessary, though? That is, why is monetization such a big deal for a communications platform? A marketing competition? There's no inherent need to participate in that.
A communications platform is useless if its user base is small; who will you communicate with? People have some limit on the amount of different communication platforms they can participate in simultaneously. The number one way to get more people on your communications platform is to have lots of people on it already; the number two way is convincing people to use it (that is, marketing).
Monetization is a big deal because communications service for 1.7B people is expensive, and Facebook is actually a very efficient system compared to regular telecom.
A centralized communications service for 1.7B people is expensive. Not that decentralized or federated services would be cheap, but the costs would be dispersed.
