Because their cousin is sick. Because they want their daughter to go to school in the city and move up the socioeconomic ladder. Because their parents are injured and can no longer work. These jobs require sacrificing all of your personal freedom to support others. They require enduring human rights abuses themselves to so others don't have to work this very job. The reasons why farmers are leaving their fields isn't for their personal well being at all, it is altruism.

The intensity of farm work isn't even comparable. You aren't toiling in the fields doing the same exact thing for hours every day, every month, every year like you do in a factory. Most labor happens during harvest and planting seasons, maintenance labor throughout the year is focused on improving your living conditions or other local projects, something you can't do if you are working for the factory. Unfortunately, things come up that can only be fixed with immediate or continued access to capital, so you have to send one of your family members hundreds of miles away to work in a factory to fuel an emergency fund. The problem with farm work isn't the work, it's the lack of enough pay to deal with disaster.