Why would it need to create energy and mass out of nothing? Why are assuming the energy either comes from nothing or wasn't already there. Or better yet, that nothing as a source is a problem to begin with?
Conservation of energy applies to a universe. There are no such rules written out for imaginary multiversal mechanics. The "but mass and energy" thing gets thrown in the trash long before we reach this point, we stopped talking about matters of mass and energy two paragraphs ago. It's the same as asking "but why CAN you fly in your dreams? What about gravity, what happened to it?".
They don't exist. No one can prove otherwise yet. They're as bullshit as whatever we want them to be.
Joke about my name have the "Dr" title