system
A chat on subreddit /r/NoStupidQuestions
human
They don't make money from WhatsApp. They make money by keeping you in the Facebook ecosystem.
gpt
&gt;They don't make money from WhatsApp.

Also, let's not forget that while chat is encrypted, just the statistics of use can be valueable.  
Having Stats of saying "So, 50M users used WA mostly between 8PM and 2AM. 100M used between 8AM and 3PM" and so on, can bring money , since many companies that work with studies and research for statistics could use those infos.