>It's a comparative figure, which is particularly important for underscoring the consequences of owing money in the long term.

But it's not comparative -- in e.g. mortgages, they separate out costs (e.g. "closing costs", PMI, inspection) that should rightly count towards the effective interest rate [1]. If they did the same for payday loans, they could (reasonably IMHO) break out the (far more legit) processing costs -- say, $5 in labor, $5 (amortized) for overhead like security, and then you're paying more like $20 for "interest" if you measured by the same basis as a mortgage.

[1] For example, if they loan you $300k for the home at 5% but require $3000 in such costs, then they've really loaned you $297k at ~5.05%.