Yes it is US centric cause unlike in Europe the US gave SMS and talk minutes Free. So there was no need for something else at the time. The reason why the US don't use non default apps is exactly that, they are non default. People unless given a specific reason won't change what they have already.
When Apple did iMessage it was interesting that you got all this on iPhone to iPhone and SMS which was still used by every one else. Then better options like Whatsapp and signal came along. For myself I loved Whatsapp until Zuck bought them. At that point I dropped them like a hot potato. Meanwhile with Apple's here they built a cult following since for many it just worked. Nevermind that there was something better, to them it was all there to begin with. Then you have group pressure of "Why don't you have iMessage?". Even though they know you have an android phone. There was a hope years ago that iMessage would come to android. That was until they realized it could be used as a lock in to keep people on iOS.
So here we are now. Let's hope RCS will help.