Question

how did kerela become one of the most developed country in india

Answer 1

Kerala became one of the most developed state India because it made use of human resource for its development

Answer 2

ONE of the reasons why Kerala does well on development indicators is that it has high literacy (mentioned as one of the indicators in your question details).  Once you parse the literacy data, you will see that female literacy rates are also very high, much higher than other parts of India. 

The impact of an educated mother on the whole family is well known and documented with evidence from around the world.  

The tradition of education of the girl child has been strong in Kerala. The Maharaja of Travancore established the first girl's school in the 1850s. His example was taken up by neighbouring kingdoms, most notably, Cochin. The influence of Christian missionaries who ran schools where girls were admitted also have contributed.

All of these in turn have contributed to smaller family sizes, better fed children, better education, better prospects - a self sustaining cycle that spirals upwards with each generation