You can rarely find a Nigerian adult without a bank account, even if they aren't using it frequently they still have a bank account and as Bitcoin hasn't yet been fully adopted you may just need a bank account to make daily purchase.
I don't know if you can actually carry on without a bank account, I would definitely love to go fully into Bitcoin but we still have to be realistic. But Bitcoin isn't just an investment opportunity it has even greater value than that.
Currently not all Adults have bank accounts. In fact if you think of it, the really senior citizens, the Octogenarians and even Nonagenarians have no need for it because they cannot operate one, then there are those who are in the deep rural areas where the closest available bank is miles away. So yes although bitcoin is not just for investment, it cannot yet carry out its other functions fully because e still get many people wey never even hear of am, or sabi invest in am, or to even use am for transaction.