A hypothesis is “I think x is true” or “x will happen if I do y.” It is a conclusory statement based on existing knowledge that then has to be proven and is one of the first things you learn to do in science. Asking “what happened to x” or “what is x” is not a hypothesis, it’s an open-ended inquiry. While both are useful, the hypothesis is specifically part of the scientific method. You’re proving or disproving smaller conclusions to answer a broader open-ended inquiry.