While India eliminated a lot of the feudal practices, soon after it ceased being a British colony in 1947, Nepal and Pakistan didn't change much at all. As a result, both nations have lots of poor, unhappy people. But Pakistan also had strong tribal structures, and the tribes eventually went to war with the corrupt central government. In Nepal, the tribes didn't have that kind of military clout, but the conditions were right for the kind of grass roots campaign that worked so well in Cambodia during the 1970s, China in the 1920s and many other places where the government was unable to suppress well organized bandits.
India has problems with Maoists as well. There are portions of eastern India, where large tribal populations live, where smart, well organized and dedicated Maoists have built similar armies via recruiting or kidnapping teenagers, and extorting enough money to keep the kids fed and busy. Fortunately for India, they have fewer armed Maoists than does Nepal. As a result, while there are currently about 800 deaths a year from Maoist violence in India, there were several times as many in Nepal.
To survive, the Maoists have to work the media, and leftist politicians, to gain sympathy, and to diminish any police or military operations. This has worked in both India and Nepal, although leftist politicians and the press are becoming less helpful. After all, the ultimate goal of the Maoists is to establish a communist dictatorship. Although Maoists have expressed an interest in negotiating and settling for less, no Maoists have actually done this. The only examples of Maoists getting what they wanted, were China in the 1960s and Cambodia in the 1970s. Those two events killed some twenty million people.
The Maoists of Nepal revealed that their active duty guerilla army comprises some 36,000 people, of which about 10,000 have weapons. The Maoists have been around for eleven years, and were organized by middle and upper-class political activists. With good leadership, the Maoists set out to use popular discontent with the feudal condition of the Nepalese culture and economy, to recruit an army heavy on teenagers, and the use of terror and extortion to keep everything going. This is a classic strategy, that has worked for centuries. The Maoists had low overhead, it only cost them about $250-300 to keep an armed Maoist in action for a year. Extorting cash and goods from local officials and businesses provided enough cash to hire sufficient muscle to keep the army and police at bay. When the government realized they had a really serious problem, the Maoists had become too numerous to quickly eliminate. A force of 10,000 armed fighters, in a country with many jungles and mountains to hide in, and a population of 26 million, was a force to be reckoned with. The government spent most of the last two years arguing amongst themselves. Meanwhile, the Maoists cancelled taxes and rents (to landlords, who owned most of the land and leased it to many tribal peoples) in areas they controlled. The upper class in Nepal is largely composed of Indian families, most of whom moved in centuries ago and subdued the many tribes the still comprise the majority of the population.