They have a captive audience of just about everyone. They can put things in the WhatsApp client and everyone will see it.

Almost everyone has WhatsApp, much more people than have Facebook. And Facebook is slowly dying.

Facebook bought WhatsApp (and also Instagram) so Facebook the company has a future. Because it’s not quite sure Facebook the network has one.

This is called commoditization. Pretty much every company does this.

You offer a product that would normally be paid, for free and gain market share. Then you build a business on top of that customer base you created.

That's where WhatsApp comes in for Facebook. They've gained huge market share, now they can attract businesses that want to sell directly to consumers. This is pretty handy and common in countries like Brazil.

Before people start shouting against Facebook, I'll reiterate that every company does this: - Microsoft did by driving PCs' prices down so they could gain software market share. - Stripe does it, with things like Stripe Atlas. They commoditize creating your own business by making it very simple. The idea is that [some of] those new businesses will eventually use Stripe and will help the company grow.

This is a pretty common pattern.

Facebook has monetization plan for whatsapp in India. In partnership with Reliance Jio, they are launching an e-commerce on whatsapp! So all of these strategies including publishing ad in newspapers makes sense in that regard

The only rationalization I can imagine is that providing whatsapp potentially prevents the emergence of a competitor who steals users from Facebook through their chat service.

Facebook wants to get businesses to use whatsapp and that's where they will get value. Payments + services for businesses will subsidize the E2EE personal chat.

Not that I buy what they're selling in your fourth point for the long term, but I imagine ads like on Facebook.