VR adoption is still relatively low compared to flat screen usage. The key here is price. If you look at when monitors went from CRT to Flat panel the original adoption rate was low due to the high cost of the flat panels. Now you cant find a CRT monitor unless it is sitting on the side of the road. As prices fell adoption rate increased. This is what we are waiting on for VR. Good, high quality VR is expensive. Cardboard and its plastic brethren are cheap if you have a phone to run them but dont offer the same experience as the big VR HMDs (Vive, Rift, WMR). The big HMDs cost a lot more and require a beefy machine (Which most avid PC gamers should already have) Rift sells more due to being less costly than the Vive, hence the significantly higher numbers in the pole.