Physical Danger
You basically do everything that could make a job dangerous. You operate heavy machinery. You spend all day working around massively huge, ridiculously loud aircraft with nothing more than a pair of noise-blocking earmuffs and a shiny nylon vest.
You drive a cart on a highway that you share with airplanes. That's almost as bad as driving a cart next to a herd of elephants—except you can't distract an airplane with peanuts.
You lift heavy things day in and day out. And depending on where you live, you'll probably encounter some seriously extreme weather conditions. For those in the heat, it's even hotter on the tarmac; for those in the cold or rain, good luck not catching hypothermia. People who work double shifts in desert climates might even get cooked during the day and frozen after dark.
Flying may be the safest way to travel, but that doesn't mean anything to the people on the ground running around the wheels.