The applications for batteries were painfully obvious long before li-ion batteries were a thing.

Rechargable batteries have been around since the 1850s. The idea of "battery, but smaller" isn't exactly a hard sell when you already have devices with huge NiMH / NiCd battery bricks attached to them. Just look at the laptops and mobile phones from the 90s!

On the other hand, VR is almost entirely a solution looking for a problem. VR headsets have been around since the 80s. Sure they sucked, but the fact that there still isn't a killer app forty years later should be a good indication that the concept itself perhaps isn't too attractive.

VR development is driven solely by Facebook's desire to sell VR, not by customer demand for better VR headsets. If the current headsets aren't good enough, a 50% lighter / faster one isn't going to make a difference.