Very similar to asking why you should use React when Angular came first. A-Frame and React VR represent different styles, and they both excel at different scenarios.
If you're building a relatively static scene, or really like the idea of having a small amount of HTML with super powers, then run with A-Frame. I think it's a fantastic product.
If you know React, find React's declarative style of programming desirable, or have a more complex, stateful application, then React VR is your best bet. It's true that the A-Frame community is larger than the React VR community, and there's more code out there for it, but React VR integrates with the entire history of React tooling and libraries – React VR doesn't need a specific data management or navigation library, because it's just React. Our goal is to take all web developers who know React and enable them to become VR developers as well.
Andrew from React VR here. We've been gathering developer input for months as we tweaked APIs and prepared for a 1.0 release, and now we're excited to open up things to the broader community for contribution: https://github.com/facebook/react-vr
Tokens and bullae are fascinating pieces of early human economics, but the core of Schmandt-Besserat's theory -- the idea that certain tokens developed into carvings of words and concepts -- is widely discounted by archaeologists today.
For one example of why, consider the earliest depiction of the word for sheep: a circle with a cross. Sheep were one of the largest commodities in Mesopotamian trade, and yet only a handful of tokens matching that crossed-disk shape have ever been discovered. If transactions involving sheep were taking place daily, they should be among the most plentiful of tokens. These token systems are an ingenious human invention, but they should be seen as the precursors to mathematical accounting, not writing.
If you know React, find React's declarative style of programming desirable, or have a more complex, stateful application, then React VR is your best bet. It's true that the A-Frame community is larger than the React VR community, and there's more code out there for it, but React VR integrates with the entire history of React tooling and libraries – React VR doesn't need a specific data management or navigation library, because it's just React. Our goal is to take all web developers who know React and enable them to become VR developers as well.