In order to claim a capital loss on your taxes, you have to sell. No point in holding something that's going nowhere.
That stake was likely worth hundreds of thousands if not millions of dollars, but to KPCB it wasn't worth the hassle to find someone willing to pay that. They know they make a loss on most of their investments.
The purchaser collects a service fee and a lottery ticket for the random "XYZ Inc sold patent to IBM for $10 million during company liquidation."
The buyer isn't buying for tax offsets. They're buying at deep discounts because they're often the only bidder and the hope that they occasionally find themselves taking on some asset for which the sellers have vastly underestimated the value (such as some obscure patent).