SecondLife was almost there, with its own economy and all. And so did other games like Eve online.

But the problem was economy. A virtual world with a centralized economy can never get enough traction because people must trust the platform completely. Otherwise all their riches they accumulated in the virtual world can be wiped out overnight and they can't do anything about it.

This is why projects like Decentraland (over Ethereum) and High Fidelity (by the founder of SecondLife) are getting attention.