It's not (a majority of) he users' fault as WhatsApp was its own company for a long time until they sold to Facebook. I was using WhatsApp long before it became a FB company. Everyone just continued to use it as FB was mostly hands off until they started imposing changes a few years later. But like every other messaging app, once someone is using it forever, it's hard to move away from it because all their friends and family are using it and have no desire to switch to something else.

Incorrect. In certain European countries it's widely used, in others not so much. In the ones where it's more widespread, I still think 99% is very much exaggerating. Maybe you didn't mean it literally?