I think what you're missing is that the blockchains depend on network effects to function. They scale naturally with adoption, being decentralized. Facebook does not scale naturally with adoption, because it depends on its own private funds to purchase more servers and bandwidth to handle the scaling, whereas decentralized technologies do scale easily because each player pays for their own equipment.

So, no, they (blockchains) won't be "maintained by a single player". The code may be centrally maintained, but not the network, and it is the network that holds the value. The crowd is fickle, and bitcoin could turn to nothing tomorrow based on the whim of the crowd. Still, the internet has this same quality, and it's still going strong. It (the internet) is simply too useful to be discarded. It remains to be seen if bitcoin is that useful as well.