As a profession, many people work to make a living.
Many senior crew members are sailors because they have studied this major. Before they go to college (or technical secondary school), they don't know exactly what to do.
Some intermediary companies will recruit some people in poor areas, and after several months of training, they will be sent to the ship to be ordinary crew members. This is a minority.
There are many people in coastal areas who go aboard as crew members, and the wages of crew members are relatively high, so being a crew member is not necessarily a person with a hard life.
As for the danger, I think it's much better than going to the coal mine.