The multiverse stuff has been hanging around in the cultural subconscious for a few years now. Adam Curtis would make a montage of how these movies line up with what's going on in the world.

I think people are disappointed in how their lives turned out and imagining alternate realities makes them feel like they are fulfilled somewhere out there, even if it's not here. Or they like to imagine different paths they could have taken. It also takes the for granted the idea that our lives are deterministic based on a series of variables or individual choices, which lets us escape the idea that our society is oppressive on purpose. It jives with liberalism in that way.

Obviously multiverse stuff has existed in fiction for a while, but it's gotten a lot of popularity recently.