What do Keralites do for living?

I am from Bangalore. I went on a 1 week trip around Kerala. We were traveling from Munnar to Alleppy. One thing I observed were big houses on with large yards, driveway, gates etc. The gates of many of these houses were open for some reason. Some were beside farmlands, some weren't. What do these people do for a living to be able to build such big homes? I have seen really few houses like those even in Bangalore. There are big one's but not like Kerala with the big yard, driveway etc.. sort of like movies.