"Why did the projected explosion of technological growth everyone was expecting—the moon bases, the robot factories—fail to happen? There are two possibilities. Either our expectations about the pace of technological change were unrealistic (in which case, we need to know why so many intelligent people believed they were not) or our expectations were not unrealistic (in which case, we need to know what happened to derail so many credible ideas and prospects)."
Physics is a harsh mistress; our expectations that the laws of physics could be overcome by technology was unrealistic.