They are not worth to be payed a decent wage because they require no skills and are easy and quick to learn. The potential employee pool is extremely large because of that, because everyone can do it. They also pay little because the profit margin is slim, as usually these jobs involve products in the lower price range. Increasing the wages means increasing the prices, making the point of cheap fast food restaurants for example moot. Supply and demand. Pay the people more, and prices go up. This increases general cost of living, and that nice higher wage is worth the same in buying power as before.