WhatsApp wouldn't exist today (at least not at the current scale) had Facebook not bought it. They have operated for over a decade now, serve 2 billion users, and have made close to zero revenue the entire time.
Sure, things like adding group video calling massively increased their costs, and they probably couldn't have done it without facebooks help, but without that they probably could have survived on 1 ad message per year, or on $0.50 per year (which they actually charged for a while).
> WhatsApp’s six-month revenue for the first half of 2014 totaled $15.9 million and the company incurred a staggering net loss of $232.5 million, though the majority of that loss was for share-based compensation.
WhatsApp was always running on VC cash.
In my country (Argentina) it became a de-facto platform for selling for small businesses, grocery stores and restaurants. There are a couple of 3rd party e-commerce platforms that generate the order and then simply drop it through WhatsApp so you can continue through there and handle the payment manually.
... There are many ways in which WhatsApp could have explored making profits. Facebook simply made it stagnate.
WhatsApp can actually be monetised successfully by a company like Facebook.