Back to the Future was a massive surprise hit in 1985. So much so that the studio had no choice but to make a few more - and to work with the open-ended final scene they set themselves up with in the first one. Back to the Future Part III does raise some questions. Like why doesn’t the Doc just leave town or pay Mad Dog the money? Why did the doc build another time machine? Was Jennifer really unconscious for two whole movies? (thetvdb.com)