Sometimes, yes... but often, those new hires who quit are simply doing the math. If you are just looking for a paycheck, being a package handler is a terrible choice. If you need the insurance, or want to make a career of it, and go driving, or are there for the tuition reimbursement... it can make sense. Otherwise, working 18 hours a week for just over minimum wage, especially doing heavy labor, vs stocking shelves at Target, etc... for 20 - 30 hours a week at $12 doesn't make alot of sense. There is no honor in working harder than necessary, for less money than necessary. It doesn't make you a hero, it makes you a sucker.
The ones that stick around the hub are those that are there for something other than the paycheck. Sure 15 - 20 years ago it was hard work for fair pay. It's not 1990 anymore, however.