I think it's a case where people without much background in physics try to use intuitive, "common sense" thinking. In our grounded world, we step or move by "pushing against" things. If a giant hand picked up a car, its wheels would cycle uselessly with nothing to "push against". The fact that the gas in the rocket "pushes against," not the atmosphere but the rocket itself, isn't as obvious.
Then there's the misconception that a craft in space would have to endlessly burn fuel for propulsion, rather than coasting with no friction. A mind expecting Earth conditions will expect the craft to come to a halt with no further propulsion, and it's hard to rewire one's thinking to accept this.