This sort of analysis is very surface-level I think. My impression is WhatsApp offered that by running on VC money and had no plan to run an actual business. That's not a question of focus. It's an unsustainable, please monetise me later land grab.
Zuck Says Ads Aren’t The Way To Monetize Messaging, WhatsApp Will Prioritize Growth Not Subscriptions
"Monetization was the big topic on today’s analyst call after Facebook announced it acquired WhatsApp for a jaw-dropping total of $19 billion. That’s $4 billion in cash and $12 billion in stock, and it reserved $3 billion in restricted stock units to retain the startup’s employees. But Facebook CEO Mark Zuckerberg, CFO David Ebersman, and WhatsApp CEO Jan Koum all said that won’t be a priority for the next few years. And when the time does come to monetize aggressively, it won’t be through ads"