It comes back to money: a pure fiat currency like Bitcoin is only worth what its users believe it to be worth — otherwise you’ve just paid a lot for some random bits. That means that everyone who has spent real money in that space has a vested interest in getting other people to buy in. They’re not going to benefit from your use of a database or PKI and thus won’t consider those as possible solutions.

This works as well as any other system designed by the sales team.