I think one of the bigger reasons was something the article touches upon - image sharing. Internet connections can often be sketchy, and Whatsapps compressed im

I think one of the bigger reasons was something the article touches upon - image sharing. Internet connections can often be sketchy, and Whatsapps compressed image sharing often ran circles around its competitors. The other reason was the identity to phone number mapping and the ease of setting up communities with those identities. Yet another reason was you didn't need to separately pay for a mobile data package and a SMS package anymore - WhatsApp replaced SMSes and it fit frugally into the data plan. I know that in my circles these played a big role. Reason 1 was especially significant for my parents/older relatives since my conversations with them are not text heavy (maybe them getting used to a device to type in for casual communication is a factor) - we often share images, family photos - and WhatsApp killed it in this niche use-case.