While receiving social security disability, why is there a two year waiting period?

According to a July 19, 2009 article in the Dallas-Ft. Worth News, “When Congress extended Medicare coverage to people with permanent disabilities in 1972, it also established the waiting period. Lawmakers added the wait to hold down the cost of the new government benefit, avoid overlapping with private insurance and make sure Medicare would be available only to people whose disabilities were long-lasting.” The primary roadblock to reducing or eliminating this waiting period is money: according to the Congressional Budget Office, eliminating the wait would cost the federal government $6.8 billion the first year and $110 billion through 2019.