That wasn't the question. They assumed that it did have an end when they formed their question of what happened when you reached the end. Some thought you'd fall off. Some thought there was a big monster that ate you. They were wrong to make that assumption, and their question became meaningless. As they learned more, they understood why. There was a paradigm shift.
You assume that the somethingness of the universe, as we perceive it, must have a cause, a beginning, and an end in ways that we completely understand. The paradigms in which we view time and causality, have changed relatively recently in modern physics. Given how little we understand of the universe, and the rate at which our understanding changes, you're very likely wrong in making your assumption.
