This is untrue, the US carriers had a "cross-carrier" consortium that had built most of its own RCS stack, complete with animating dots when the other party was typing, and good image and video support. But Samsung refused to use it (not sure if Google was bribing them in the background) so it got killed in favor of supporting Google's flavor of RCS.
> In October 2019, the four major U.S. carriers announced an agreement to form the Cross-Carrier Messaging Initiative to jointly implement RCS using a newly developed app. This service was to be compatible with the Universal Profile.[34] However, this carrier-made app never came to fruition. And later, both T-Mobile and AT&T signed deals with Google to adopt Google's Messages app.
