One point;
Whatever objective statements from Science [in this case Physics] are based on intersubjective agreements within the specific group of sufficient scientists involved.
The objective statement of the existence of a multiverse from a group of Physicists [scientists] is thus grounded on an intersubjective consensus, thus fundamentally subjective.
The majority consensus of this group of physicists many total up to only 50 leveraged upon compliance to the Scientific Framework and System of obligatory processes.
To add;
undeniably useful, there is nothing great with objective scientific theories.
According to Popper POV, scientific theories are at best merely polished conjectures.