> Facebook first got into the data-sniffing business when it acquired Onavo [..] to learn that WhatsApp was sending more than twice as many messages per day as Facebook Messenger [...] and to spot WhatsApp’s meteoric rise and justify paying $19 billion to buy the chat startup

This makes a lot more sense now. At that time the tech sphere was surprised at the price tag which is expected as people outside Fb perhaps didn't have these metrics.