I worked on the design of wireless USB chips around 2008 - 2010. They worked - you really could get USB 2.0 full rate connections wirelessly and we had some neat demos.

I would say the major problem it had with adoption was that wired USB also provided power. (A lot more people use usb to charge their phone than to sync their phone.)

So great - wireless connectivity... but you still have to plug the device into a cable at some point (or have replaceable batteries), which makes the value proposition a lot less clear.

Beyond that it suffered from the usual adoption chicken-and-egg problem. Laptop manufacturers didn't want to add it because it was an expense that didn't drive sales since there weren't any must-have peripherals that used it, and peripheral manufacturers didn't want to make wireless usb devices since they couldn't be used with a standard laptop (at least not without a WUSB dongle - which raised the cost).

Still, very fun stuff to work on.