What was the reason that astronomers named Pluto a dwarf planet?

Of course there's something wrong with it. It has a wonky orbit and low mass, as do other rocks floating in the solar system. They had to make a compromise between what people (both plebeians and astronomers) have come to expect and what people will have to accept in the future, bearing in mind the speciality of planets in exosolar research. An arbitrary exception isn't very scientific. I'd say it looks to be an adequate comprise, with all parties dissatisfied.