Why does the HK416 exist?

The AR15 is one of the most popular rifles in the world, and it's proven itself to be a reliable weapon. But this wasn't always the case. There was a time, when the reliability of AR15s were questioned - and in some cases not without merit. As a result, a number of weapons were developed with the intent of replacing the AR15. And perhaps the most notorious of these, is the HK416.