[JeremyNT]

This thread basically sums it up:

* Apple is really popular in the US

* Apple users tend to rely heavily on Apple's default applications

* Apple's messaging app is the default, and works fine with other Apple devices, but sends shitty SMS or MMS to non-Apple devices

SMS would disappear tomorrow if Apple adopts RCS.

And if they allowed iMessage clients on other platforms, they could corner the entire messaging market.