Did you know people below the poverty line would by $20 S40 feature phones just to be able to run WhatsApp? The other 2G phones cost less than half that amount, but you had to pay $0.1-$0.2 per SMS sent, in that light, spending $1 per year for WhatsApp's unlimited messages on a PAYG data package was a steal.
So no, I am not nuts, you just didn't think through the value proposition.
Network effects, similar to present-day Facetime in the US. There's Zoom and Google Meet, but if your family and friends are already FaceTiming, you're pressured into buying a iDevice.
There's a surprisingly number of people whose usage of the Internet is exclusively through WhatsApp, and may not even know what a "browser" is or how to use it to get in touch with their contacts.
Are you nuts?