This is due to Inflation.
As time passes, prices of commodities, labor, and services tends to increase.
In order for a healthy economy to grow, country's try to limit inflation and keep it at a minimal.
However, deflation, which is the exact opposite is avoided as it can hamper in the overall economic growth of the country.
The example of Pizza hut shows how, over such a long period of time, the prices of services and commodities can increase so much.
