It was Risley, the commissioner of the 1901 census of India who introduced so many castes. It was the game-plan of British as part of their divide-and-rule policy:
“Risley wrote that he wanted his 'scientific' research to 'detach
considerable masses of 'non-Aryans' from the general body of Hindus'.
He adopted the popular Race Science measurement methods used by French
experts, according to which physical traits, such as the size of the
nose, were a more reliable measure than skin color. Risley was an
enthusiastic champion of the newly fashionable science called
anthropometry, which measured various parts of the head to
characterize different peoples. He used his measurements of people in
India to conclude that there was a remarkable correspondence between
two kinds of data, namely, (i) the 'gradations of type' as brought out
by certain indices of head measurements, and (ii) the 'gradations of
social preference'. This, he wrote, 'enables us to conclude that the
community of races, and not, as has frequently been argued, the
community of function, is the real determining principle . . . of the
caste system'. His 1891 ethnographic study of Bengal became the model
for similar studies across India. His program measured Bengali heads
and noses with calipers in order to establish hierarchies based on
physical body dimensions.” “Based on Risley's research, Indians were
classified into seven major races located on a linear scale, with
Aryans and Dravidians as the two opposite poles. He also organized
'social types' into seven groups. To protect himself, he wrote
numerous disclaimers against blatant racism, and against taking things
too far. Yet that was precisely what he did and wanted others to do.
He claimed that according to his data, 'the correspondence between the
two sets of groupings', namely, the seven races and the seven social
types, was sufficiently close. He thereby concluded that Indian tribes
had turned into castes. He described the various tribal types in the
order of their primitiveness, positioning the Dravidians as the
lowest, assigning manual labor as their 'birthright', along with human
sacrifices to a goddess.16 Those tribes that had developed
professional specialization became castes, while those that had
remained in a limited geographic territory were still classified as
tribes.”
“As the commissioner of the 1901 census of India, Risley wrote the
section on caste, which was published in the highly influential
Imperial Gazetteer of India, and became the template for academicians
and colonial administrators to do their studies. He decided that
Indians consisted of 2,378 main castes and tribes (with sub-castes),
and 43 races. To implement his hierarchy of castes, he decided not
to list them in alphabetical order in the census forms, but rather in
order of what he considered 'social preference' based on his
evaluation of 'native public opinion'. Thus, a hierarchy was
constructed and made official. The bewildering array of castes he
listed, from which each person was required to choose when filling out
official government forms, ran into so many pages that it 'gives so
much trouble to the enumerating and testing staff and to the central
offices which compile the results.” “Risley translated the dharma of
various jatis as 'race sentiments', and made it his ambition to
scientifically prove that a comparatively pure 'Aryan type' existed in
North India. His obsession with noses caught on with other colonial
administrators. For example, noses of Indians became the subject of
scientific inquiry for Edgar Thurston, author of the voluminous Castes
and Tribes of Southern India (1909). Thurston even used his 'Lovibond
Tintometer' (originally an instrument for quality-testing in
breweries) to measure the racial features of Indian villagers.”
The above are excerpts from a book 'Breaking India' by Rajiv Malhotra.