Bitcoin's original goal was "electronic cash". As was M-Pesa's. They solve the same main user problem: payment. It's true that they're implemented in completely different ways, and with different philosophies. But my point with M-Pesa is that there are no inherent barriers to digital money. If Bitcoin had been useful to a broad audience, it could have had adoption similar to M-Pesa's. It hasn't, and at the rate it's going, it never will.

Using already existing fiat currency is probably why it is successful.