If by "real wages", you mean "wages adjusted for chained CPI" (this is what most people mean), the answer is because the basket of goods used to compute CPI has become larger.

I.e., consider the following scenario. In year 0, there is one good - food. A basket of food costs $100. In year 1, medicine is invented, and the cost of food goes up to $101. Inflation is 1%.

The basket of goods is modified to reflect the invention of medicine, and is now comprised of 50% food, 50% medicine. In year 2, the cost of medicine increases 10%, and food decreases by 2%. Chained CPI now reports an inflation rate of 3.45%. Is life worse in year 2 than in year 0? (This is a combined 2-year inflation rate of 4.5%.)

Of course not. In year 2, you are paying $99 for a basket of food. In year 0, you are paying $100 for food and Medicine doesn't exist.

I have yet to see anyone construct an inflation measurement based on a fixed basket of goods (which is held constant over the years) that shows real wages have gone down.