For a lending charity, rate caps reduce interest income. This, in the long run, depletes the charity's capital base. An interest rate (>5%) lower than the expected default rate (~10%), as it appears to be here, amplifies the effect. That said, the decision could make sense. If "non-usurious lending" increases donor interest enough, it could offset the capital depletion effect.
I'm fine with short term loans at 25%. As you say, $50 at 25% for a month is $1.04. The problem is when a $1-5 fee is applied on top of that, giving interest rates >100% annualized. That's the kind of usury which has been common in the US payday advance industry (although better now in most states after regulatory action), rent-to-own, etc.