Ambitious Keralites move out of the state to set up businesses. The ones who remain usually get rich through a mix of unethical businesses, political party connections and corruption, or the gold and money-lending businesses (which were inherently shady). Keralites are either highly ambitious, in which case they go to more welcoming cities such as Delhi, Bangalore and Chennai, or extremely lazy, in which case they stay at home and abuse the welfare state. The welfare state is so abused by lazy government employees who will do anything to block you from setting up your business. And if it isn't them stopping you, it's the pesky political parties who will send their goons after you to charge for every task.
https://en.m.wikipedia.org/wiki/Nokku_kooli
For instance, the richest Keralite, Yussufali MA, made his fortune in the Middle East. His sons-in-law, both billionaires, as well as KP Basheer, Ravi Pillai, PMC Menon and Mohammed Ali of Gulfar made their fortune in the Middle East, all of whom are silent billionaires even most Indians barely know of. Vivek Ramaswamy's parents were from Kerala too, as is Thomas Kurian (head of GCP).
If you look at the West, Keralites are increasingly taking spots in the medical and healthcare sectors, especially nursing, and now even the education sector. There are Keralite teachers in the oilfields of Midland, Texas, because most people are otherwise not ready to work there. Some of my neighbours relatives from back home were even working in Afghanistan for the USG, making bank for working in a warzone. The only groups that are more or equally as prominent as Keralites worldwide might be the Gujaratis (the Patel motel guys and diamond merchants) and the Jews.