The article sort of addresses the consumer motivation for choosing prepaid cards over traditional banks:

    During Servon’s research working as a teller at a check
    casher and payday lender, consumers told her that the fee
    structures of nonbank alternatives were more transparent 
    and predictable than those at conventional banks—crucial to 
    anyone living on a budget.


    Prepaid cards offer this predictability, and over time 
    their reputation for transparency has improved.