So they dont use RCS Universal first, which means the vast majority of folks fall back to MMS/SMS.
Having it as a fallback means it literally doesn't matter what layer its at, as long as its at a layer before the more broad ones.
Google tries to use RCS-Google. If it fails to connect,
It uses RCS-Universal. If it fails to connect,
It uses MMS. If it fails to connect,
it hits SMS. If it fails to connect.
It fails the message send and queues up for later.
IE. If the Person isn't using RCS-Google. And their carrier supports RCS-Universal. It uses Universal. It doesn't matter if its not the first or not if it gets caught on the next layer anyways. And if Apple implemented RCS-Universal as a fallback. They would get caught on the second layer for both Android and iOS since the fallback pattern for iOS is:
Apple tries to use iMessage. If it fails to connect,
It uses MMS. If it fails to connect,
It uses SMS. If it fails to connect,
It fails the message send and queues up for later.
And sure. For a good ~40% of people they would fallback all the way to SMS. But you are literally just in favour of the statis quo becaue Apple doesn't support it. Eventually society is going to need to move on from SMS. And are Apple users such technophobes that you want society to continue using an obsolete standard that barely worked when it was introduced, 20 years from now?