The Oculus Rift was originally designed for standing or seated VR experiences only. Oculus thought that roomscale was impractical and that there wasn’t enough demand for it.
If you’re cynical, I suppose it’s possible that Oculus screwed up its logistics and is just using this as an excuse, but based on the chatter among Oculus Rift forums, it appears that there really is a lot of interest in the sensor.
In any case, I ordered the third sensor as well, and when I receive it, I will post about whether it makes a big difference. In the meantime, I have been able to use two sensors for roomscale VR.
Oculus Touch Review: the Wait is Over
Oculus Rift Review
Oculus Rift headset cable extension for under $20
A safer and more convenient way to store your Oculus Rift and Oculus Touch
How to use Oculus Rift and Touch for roomscale VR with just two sensors
Using Oculus Rift and Touch with HTC Vive games on Steam: how well does it work?
Oculus Rift and Touch may work better in USB 2.0 for some PCs
Oculus Touch Impressions
HTC Vive Review