Same is true for most of South America. In Brazil, iphones are very expensive luxuries, so the majority of the population had to deal with android phones. Which google, in their infinite wisdom, never made a decent messaging app that lasted more than 1 year.

Whatsapp had this great feature that it let you find contacts by phone number, plus you got to talk infinitely as long as you had internet, so the transition was very easy for people moving from feature phones.

In a very short time, the app reached critical mass. If you insisted on not using whatsapp, people would just ignore you, the hassle of having to use another app or, god forbid, sms you (sms used to be charged per message sent) was just not worth it.