They exploited the country, kept their family prosperous, and kept the nation in darkness. They caused hundreds if not millions of Nepalese to die in foreign great wars, sending them as mercenaries, and in turn earning what not from their British overlords.
The current political situation is an outcome of the Ranas and shahs. The delibrately kept most of the Nepali people lack of education and opportunities, so that they could not challange their status-quo.