That is because you are not in the U.S.A.
Never had a problem with
Google Message RCS since roll-out in June 2019 in the U.K. and the same for the Samsung Message app based on it.
Google got fed up with
U.S. carriers stalling and blocking the roll-out of free RCS and by-passed them... so it comes as no surprise that after a
global roll-out by Google Message RCS, that the U.S.A. is experiencing continued issues
14 months after launch in the U.S.
One possible explanation is that U.S. carriers see RCS as a cash cow and want to control it to enable them to monetize it and generate more revenue... perhaps from advertising or from big businesses who wish to promote themselves and their products using RCS.
Whichever way you look at it... it does seem strange that Google Message RCS and Samsung RCS that it is based on, works worldwide but not in the the home of Android and Google.