Not true - that loss was based on employee compensation due to the size of the deal and realized stock appreciation. WhatsApp could have covered operating costs indefinitely from user $1 payments.
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.