Why would you try to buy all the bitcoins from one person, when you can start a new chain?
You may not have the required knowledge.
certainly it would be cheaper to hire someone who has it.
IMO this is a great thread to illustrate the fundamental problem with fiat currency whose only demand is some kind of Keynesian beauty contest.
Note a currency backed by something people actually want does not have this logic problem; if one person had all the corn/oil/rice in the world, people would still be willing to pay for it at a reasonable price. But if somehow, someone collected
all of the USD in circulation... people would just say "um no thanks, we'll just make our own money".