I think he would argue it carries the least metaphysical baggage as the worlds exist in the equations we have, unlike things posited by other interpretations.
But I think it's a tough position, given that relational quantum mechanics also works "out of the box" and doesn't require ontological realism and a deeply speculative metaphysics.
Sean Carroll discusses this with Carlo Rovelli in two separate Mindscape episodes.
I'm both cases different observers observe different results.
IIUC the "worlds" on the many worlds interpretation is just a convenient way to talk about the relationship between an observer and the possible states it can observe after the system and the observer have been entangled. The emergence of a world branch is not something that happens at some specific moment in time. This is also why branching can be viewed as happening at superluminal speeds, because it's not a physical phenomenon, just a shortcut for us to use to discard states that are no longer accessible to us.
Whether that makes the many worlds interpretation more useful or less useful, it's a matter of context. However I have the impression that most people who oppose the view (e.g. citing how much more baggage it requires etc) fundamentally come from the mental trap of thinking that a conscious observer had a unique stream of consciousness and that anything that deviates from it would be inconceivable because "we don't experience it"
I am sympathetic to the idea that no one interpretation is 100% correct and that we shouldn't be deeply attached to any of them. Each may have its usefulness in different contexts. Independent of that, some interpretations more accurately describe the quantum world than others, surely.
I'm an avid listener to mindscape podcast and read of his books, so I'm likely "indoctrinated", as I don't really know much of these things.
But I had the distinct impression that Carrol believes that all there is is the wave function of the universe and everything else (including the many worlds) are emergent phenomena. In a way many worlds are "real" in the same way that "chairs" are real.