You're right.
I do not know that they (weren't) approached by MS, Google, or Facebook.
I do not even know that CSpace failed to come up during their search.
It is conjecture on my part.
But I highly doubt that these major companies wouldn't have come across them if they were interested. 3DIcon has an entry in wikipedia under volumetric displays, and we all found them, and we're not a team of professionals who work day in and out on making 3D displays.
End of the day, theres billions of dollars being invested in very different technology.
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