This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
It's just how the language is designed. And there are pretty good reasons for the design - you'd run into problems with overloaded methods where it was ambiguous which version was called. But fundamentally, this is one of those questions where the answer is "because that's how it works".