When the NSA was talking about metadata collection, they said it was more useful than actual data. Likely because it's already computer consumable, and less dense.
If FB gets your contact lists, and sees who you message, how much, and when, that's probably a hugely valuable commodity to them.
However, metadata is always what it is. If you have someone who is distance 2 from 20 people who died unnaturally, but not distance 1 - that person is likely related to their untimely death.
The reason metadata is useful is because, unlike the text, it is generally required to be unobfuscated to 3rd parties for the communication to be useful to the 1st and 2nd parties.
Just to be clear here, is this your speculation or a known thing?
In India, the popularity of whatsapp is insane. They could run it worldwide by just showing ads to like half of Indian users
Obviously, I have no evidence for making such a claim. What I know is
1. Facebook's reputation with regards to privacy.
2. The fact that they paid 20 billion dollars to buy a product without a monetization model. (Which is 20 times more than they paid for Instagram by the way.)
3. Whatsapp's founder left the company after the acquisition due to privacy concerns.
It's enough to be more than suspicious.