Why was steerage considered the worst accommodations on ships traveling from Europe to America?

The people in steerage were at the bottom of the ship and below water level. There were no Windows, no rooms, and very little of anything else. The ships in the 1900's divided decks according to classes of people. The decks were separated with locked gates and the upper deck people who paid the most for passage never met or saw the people on the other decks. The immigrants below were locked in so they couldn't have access to the upper decks. They were considered the poorest dirtiest people on the ship so we're sold the worse accommodations.