There are short and long stems:
What effect does changing the stem length have on my bikes handling
There are flat bars and there are curved back bars for comfort upright position:
There even seem to exist bikes with no stem (apparently called "with forward geometry"):
But I have never, ever seen a bike with stem, going back from the headtube towards the rider. Such a setup would provide extremely wide wheelbase, which seems to be a good idea in some scenarios. Why is this geometry never used?