Because they pay under $20/hr, offer no health insurance, dental, no vacation, termination at will, and little possibility for promotion or advancement of skill

Because they pay under $20/hr, offer no health insurance, dental, no vacation, termination at will, and little possibility for promotion or advancement of skills. Half of this is mostly true, the other half is mostly not true. Tons of major companies in the service sector offer their employees (even their part-time employees) health, dental, and vacation. And employment should pretty much always be termination at will, unless the employee is under a contract and can't leave whenever they want, or is fired due to a protected class, whistleblowing, etc.