Not a historian, but my understanding is that there was widespread crop failure, which led to many people fleeing to major cities to search for a better way of life. Many of these people traveled by boat, which led the home country to view them as sea people. The influx of immigrants further strained the dwindling resources of the home country due to the aforementioned crop failures, which then led to a collapse of many of the cities. Which in turn caused more people to flee to other cities

So to answer your question, I don’t think the sea people were really even a singular group people, it’s just an umbrella term for immigrants that were fleeing from their home