You know why? Because Acton and Koum arranged the carrier deals prior to the acquisition. That's what Zuckerberg bought, to enlargen his war chest. It's not his product, it's something he effectively stole
People sought cheaper alternatives, and for a while several messaging apps were used, but WhatsApp was so convenient compared to everyone else (using the phone number as username, no password required, was a genius move), that it was already becoming the standard before Facebook came and acquired it.
Carriers noticed their error eventually, and stopped charging for SMS, but by then it was too late. They even tried using the tribunals to block WhatsApp, without success, and technical measures to degrade WhatsApp's protocol and block audio and video calls on it, which also failed legally. So they eventually relented, and now offer packages like "n GB/month plus free WhatsApp!!!" (and in small letters: "audio and video calls not included").
Could you say more about this? I'm not very familiar with the WhatsApp acquisition, or necessarily happy about it, but at first glance I don't see what part would come anywhere close to theft.
It almost all collapsed because of an airmiles ticket which couldn't be changed.