From a purely economic perspective, it is certainly irrational to place savings into an account with a negative return. But, the push to energize a thrift culture is not simply about economic returns but also social behaviors (i.e. see Nudge on difference between Home Economicus and Home Sapien).

While we need to understand how to make the returns attractive, we can't ignore the importance of creating a savings habit. For those with no access to savings, the alternative in the form of expensive non-bank financial institutions is much less attractive than the spread between inflation and interest rates for savings accounts.

See my thoughts on this and other subjects at hearmyecho.blogspot.com