That's a gap in the market for Bitcoin to take advantage of. With the Bitcoin ATM infrastructure rolling out across the UK and elsewhere low income people can store their money in Bitcoins, and withdraw it as fiat through an ATM. There are Bitcoin debit cards rolling out too which will assist Bitcoin in taking the place of bank accounts.
People usually keep their savings in bank to earn interest on it.Keeping it in bitcoin would not serve any purpose as most middle class families need to withdraw for their everyday needs