I agree, I don't know anyone who uses iMessage.
Same here in mexico. Everyone uses whatsapp, lots of different rooms also such as our family has one. I have two contacts that use imessage or regular text message and they are both in the us.
No imessage, facetime or anything apple-centric here.
I can't speak for china but apple had a 6% market share in all things apple last time I saw statistics. I think there are a number of reasons. Price for Sure.
Nobody uses apple centric services. Ios devices are designed more for the cloud, most people do not even have internet at home. Small ciber's are everywhere, people would rather pay 3 pesos for half an hour. Even in small pueblos there are a lot of cibers.
Up toward 90% use pay as you go phone service with no internet. You can receive calls even without a balance.
For 3.00 us a month you have unlimited whatsapp, facebook, etc. Makes no sense to use text messages.
Add all of that up and balance it with the very cheapest iphone 7 being between 8-900 us and its easy to see that most people do not need one.
Now add to it the fact that there is no iphone upgrade program here. If you get one through telcel plans you will pay a big down payment plus 100. Us or so a month for a plan to cover it.
Really the only option is through places like coppel which are similar to us payday loan places in the us where you can borrow monwy or buy stuff. Then it jumps up Several hundred more for that base iphone. People making a few hundred a month see pretty easily yhat it does not "vale la pena". Not worth it.
I know this is about china but for the most part those looking through non us eyes can understand it better. 1st world eyesight is different.