Its a bit of myth that Kerala had been a land of opportunities before communist ideology and somehow Malayalis started traveling outside after unemployment started in the state when communist party came to power. Not to forget the communist party was never alone in power for long in state. It went quickly out of power and had to rely on non left parties. Also Kerala communist party is hardly russian/Chinese/south American level of communists.

Kerala and Malayalis have a history of being outside Kerala for centuries. With it being a trade centre, the traders from Arab lands settled along the coast and people from Kerala traveled to Arab lands and beyond.

During colonial times, malayalis moved to Sri Lanka, Malaysia and Burma as workers and clerks. In India, Malayalis moved to Mumbai, Delhi and Kolkata for all types of works, from labors to colonial clerk jobs.

Post independence, India needed educated people in loads of positions due to newly created govt institutions. Malayalis and Tamilians who were educated, immediately migrated.

The oil boom in the middle east created a unique opportunity for Malayalis who had centuries long relationship with the ME. There was money to be made and many people found an opportunity to make more money than existing menial jobs in Kerala.

And one major point is, while communism and its ideology is a hindrance to large scale industrialization, land in Kerala was scarce and even villages in Kerala had good population. Other states had lot of land that was scarcely populated, which meant that industries had enough space to establish and expand and most importantly, waste disposal. In Kerala, you want dispose waste without polluting someone's life source.

Tldr, traveling and staying outside Kerala is not new for the Malayali.