Billboard says it themselves. Look at some of 1999's biggest and best singles. You heard them on the radio continously and would have guessed that they reached the Top 3. All would have reached the top with a commercial single. But nobody cares.
Albums are the big deal.
Singles take a back seat on the charts, but not your radio. In 1999, only 17 radio only hits made the Top 10. The future means that Billboard will place more of an emphasis on radio charts. Pretty soon, the Hot 100 will be radio only. The chart as it is now is misleading.