Goes back to my statement that the problem is the limit of our ability to detect things. As our technology improves, we 'see' more than we used to.
There is still much more 'out there' we don't yet see.
Agree!
Though what drives the whole multiuniverse argument is GUT theoretical work (String Theory, M-Theory, etc.). Since experimental verification is very problematic, “mathematical beauty” is substituted. While this has paid off in some instances. However in those instances experimental verification had the final say! “Beauty” seems a poor thing to hang ones hat on, but for now its all they have!