Related to raising minimum wages - why is the purchasing power of our current wages always falling? If the purchasing power of $10 was constant over ten years,

Related to raising minimum wages - why is the purchasing power of our current wages always falling? If the purchasing power of $10 was constant over ten years, minimum wage would not need to go up. If the purchasing power of $10 went UP over ten years, that would be good for the poorest among us, yes?