Kerala has been traditionally rich.
Islam, christianity, Europeans incl Englishmen all came to the subcontinent area through trade relations with kerala. we have mosque which dates back to the period of prophet .
Speaking of communists govts, there was some land reforms in earlier times which lead to massive social changes. it had massive impact on social structure but it destroyed agriculture in the long run. communists were notorious for their strikes against industries and their crime record is among high.
Kerala's status as the best state was not due to party ideologies but by ppl and we had some good chief ministers from both communists and congress govts ( the only 2 govts.. we have no BJP)..
Our education system is best and literacy is like 96-98% which is comparable to europe.. now state is focussing on IT due to big human capital and a very highly qualified workforce.