There are also bussiness accounts which are really important depending on the location.
It is very hard to put a price to that, but its value is undisputable.
After that acquisition, they made it free for all and started chasing the $$$ with WhatsApp for business. And ads. No idea which is more profitable anymore. I think they'd still be able to monetize it more with WhatsApp payments and those ads in status updates. I'd definitely like to know what the numbers are looking like these days..
It was, but it was very cheap (UK pricing was £1 a year), and I believe had lots of free users anyway. My guess is that the revenue wasn't worth pursuing.
Meta isn't a charity. If they aren't making money off WhatsApp outright, the users are the value and they're making money off them some other way, encryption be damned.