Youdidit is an explanation, because it doesn't terminate the inquisition. You can then ask what caused you, then what caused the thing that caused you, and so on until you get to the point of saying "and that's as far as we know, we are working on figuring out the rest".

With goddidit, you abruptly got to the end through an escape hatch, and you are done having done no work. There is nothing that explains god, by definition, and there is no "figuring out the rest".