"Being poor is expensive" as it is said and it is a vicious cycle as well. Because not being able to pay the total upfront cost of - in the long run - cheaper solutions, they can be stuck paying smaller amounts but more in total over time. People with cashflow problems might not be able to pay in time, leading to dunning costs cutting into their budgets. Cashflow problems might make them pick single tickets for the bus while a monthly pass would be cheaper on the long run. Not being able to pay for maintenance of the car now? Pay for a more expensive repair later instead. Same goes for health issues.
Once they are able to avoid these costs for a while, they might save enough that they are no longer actually poor (albeit still at risk of becoming trapped in this cycle again when unexpected expenses appear).