If the universe is defined as all there is, what can a "multiverse" be? Just bullshit. Nobody is his right mind can say that there is "more" than all there is.
How can people get away with such bullshit? Because they have no real friends who tell them. And because such people have no bosses who tell them. And because they are surrounded by people who depend from them. And, most of all, because they do not follow reason. One scientist that does not follow reason - that might be a tragedy. But dozens of such scientists - that is fraud covered by corruption.
The scientists who talk about the "multiverse" are paid by universities, by student fees. In the past centuries, scientists worked hard to get rid of the influence of the church, and to get rid of the influence of the state and politicians. Scientists always said that they were entitled to do so, because they were only following reason. But now we have scientists who are taking advantage of the system, and who are not even following reason itself. They are fraudsters.
The universities are paying these fraudsters. The students are paying them. The deans, colleagues and students allow the fraud to go on. That is corruption.
No it is not a conspiracy. It is fraud covered by corruption. Check your own university.