Wow, that's quite a statistic--and I'm not sure how that 70% operates without banking services. Sure, you can buy food, clothes, and pay your rent with cash but where I live it's pretty hard to pay for things like utilities, internet, and phone service without having a checking account that has a debit card linked to it. I don't think El Salvadorians are using credit cards for all of that, since it's usually hard to get one unless you have some kind of bank account.
Not surprisingly, they rely on remittance and tourism, the rest of the country is dirt poor so no wonder they don't have an account with far too little money to spend on other than necessities, why having a bank account when it will stay empty? As for utilities, internet, all that, welcome to Eastern Europe at the start of the century, paying with a bank account would have been far more troubling than going to their office and pay with cash. I remember waiting in lines even half an hour to be able to pay bills.
The real question is how the hell Government is operating even if they dont have the income? I mean if 30% peeps have the bank account then only those must be tracked by IRS and get paid for taxes. Wondering how they done with the infra of city and counties in there with such low income and high population.
Do you think that without a bank account you don't pay taxes?
They tax your employees when they pay you, even if it's in cash, you pay VAT when you buy something from a merchant, just because they only deal in cash it doesn't mean you can void taxation, and in poor countries, it's usually the poor people who are not that keen on doing so, they can't afford the luxury of a lawyer and they are far more afraid than gangs of going to prison.
Besides, even countries like Argentina and Mexico were well below that level at the start of the last decade so, it's more normal than you think.