WhatsApp had 50+ employees and made only tens of millions from their $1 fee. Where are you getting $1B from? It was never remotely close to $1B. FB publicly posted Whatsapp revenue from before the acquisition. It was a pittance.

Whatsapp also only had a couple hundred million users back in 2014. So they’d have no way to make a billion even if they charged everyone. Which they didn’t. They barely charged anyone.