How do you think all the stuff managed to get there in the first place?

You’re still thinking like a meat-monkey. There are stranger states out there than one can imagine, and that’s not hyperbole. There was no causality before expansion, because there was no meaningful interactions or spacetime in which interactions can occur.

You’re always going to have a hard time imagining this, because again, you are a human. We all are, none of us can imagine states of the universe without time and space.