"Since when do those jobs all equal the same pay? "
The better question would be 'since when do those jobs all equal the same livable wage?'
Meat packers used to make such a wage, now they do not due to illegal labor. So that is why meat packing jobs are usually not taken by American citizens; do you expect them to work hard at jobs that do NOT pay their bills?
Depends on what you call a "livable" wage. If it has to enough to pay rent, food(including cigarettes and alcohol), insurance, car, and some spending money, I've heard that that is about $25/hour. How many people make that with one job? Lot's of people work more than one job or more than one member of the family works.