Magic and Tibet
Why are these books so popular? It is mainly because they seem to be about magic. Is there magic in Tibet? What is there in Tibet?

For a long time Tibet was very difficult to visit and travel in. In 1949 Tibet was invaded by the Chinese and since then has been ruled by China. From then until about 1985 western visitors could not enter the country. Before the Chinese invasion there were few visitors because Tibet is situated among the highest mountains of the world and there were no roads. Moreover the Tibetans themselves discouraged travellers. They did this partly because they didn't want the introduction of foreign religious ideas, and partly to avoid becoming part of the neighbouring empires, such as the British Empire in India or their other neighbours, Russia and China.
When people don't know much about another people they make up stories about them. For example, people often say they think the neighbouring people are cannibals. In reality, in the whole world, very few people at all are cannibals and very few ever have been. (During times of general war and catastrophe people occasionally eat dead bodies because they are starving: in Africa this may have taken place during the nineteenth century slave wars or the eighteenth century Mfecane in southern Africa. Some magicians claim, falsely, that eating parts of the human body has good effects, but these magicians are, fortunately for us all, uncommon.)
Because people couldn't go there, stories were told about Tibet, mainly made by people like Hoskins who had not been there, and especially by people in India. The stories they told were about Magic and strange religious ceremonies. An anthropological book on the subject# says:

Tibet, more than any other part of the world, has suffered from a spate of misrepresentations, distortions and downright invention in Western literature which is almost unparalleled at any time. Reading the supposed travels of the armchair authors, the strange tales of magic, mystery and spiritual wonders that are supposed to make up Tibetan life, one is reminded of the fanciful maps of ancient geographers. When they were uncertain of the features of some place or other, they would fill the space with such legends as "Here be dragones".

Anthropology: the study of human customs. # Shah, I. Oriental Magic p173
An armchair traveller is someone who writes about distant places without leaving the comfort of his armchair in his own home. Maps of Africa made in the years before the European expansion began showed headless men and lakes and rivers which did not exist. Dragones - an old spelling for dragons, mythical animals, possibly based on a large lizard found in Indonesia - the Komodo Dragon.
Similar "magical" stories have been told about Ancient Egypt (of 3000 years ago and earlier). In the case of Egypt the people of that time can't answer back. Modern Tibetans can.

The main "magical" idea of the Rampa books is that the body of an Englishman was taken over, through some magical process, by the spirit of a Tibetan Lama. The Englishman's spirit was sent to some other (spiritual) place. This is an interesting idea which has been suggested before, mostly in Science Fiction novels. Hoskins may be the first person to claim to be a transplanted spirit. A scholarly attitude of scepticism to this idea must conclude that the Rampa books provide no evidence to suggest that it really happened. Moreover, one may wonder what the point of the transformation was, as Hoskin (or Rampa) does not seem to have promoted any useful ideas in the world. Eastern ideas from India, China and Central Asia have certainly influenced the western world and Africa (though it may not be true that the world is really divided into separate Eastern and Western parts). But this influence has come through the quite ordinary methods of publishing books and giving lectures and educational courses. One good example of eastern influence is the idea of making candidates pass an examination before being admitted to the civil service. The British may have copied this from the Chinese.

Many real Tibetan monks are now living in western countries as a result of leaving Tibet after the Chinese occupation. Anyone who wishes to know more about Tibetan beliefs can do so by reading the books they have written or by attending their monasteries in India, Britain and America. Sometimes there are television programmes about them.

Facts about Tibet
In fact, from 1642 until 1950 Tibet was ruled by the lamas (monks) of the many Buddhist monasteries which were found there. Before 1642 they had kings. The chief monk was the ruler and was known as the Dalai Lama (Oceanwide or Universal Lama). The first of these was appointed by the ruler of Mongolia, Altan Khan, in 1578. Only from 1642 did the Dalai Lama,

Useful reading

I. Shah - Oriental Magic

Oriental magic (out of print?) US$

Oriental Magic