Many prominent physicists believe nowadays that there may be numerous universes, not just one. Their mathematical calculations points in this direction. Maybe there are an infinite number of universes out there; maybe they have simply made a calculation error, who knows? However, without evidence are the Multiverse ideas nothing but fantasies.
Some people believe that there are plenty of universes, but they do not base their beliefs on mathematical calculations, physics or experience. They simply like the idea. “Cool. There are tons of copies of me out there.”
Speculations and fantasies such as these can serve two purposes. For the first, they allow an escape from what is happening here and now, in this dimension, on this planet, in this world of madness.
Secondly, they can create a sense of wonder. Everything is a mystery. We have no idea of what the reality is like, really.