True, but there aren't that many different brands that make up the majority of formula sales, for babies who don't have allergies or other special requirements.
Of course, the food bank very well may not have ANY formula available to give, let alone the brand that the baby needs/is used to.
However, having to say "I'm sorry, we don't currently have any Aptamil in that we can give you" is worlds apart from actively making it known that you don't give formula to needy parents, because of an official policy giving the clear message that they are being bad/irresponsible/neglectful parents by not giving their baby the breastmilk that they simply may not have available to give. Of course, more privileged parents, who can afford to go and buy it, can just get it from their local shop without any judgment at all.
When people are underprivileged and already down on their luck, it's just another kick in the face to a loving mum who cannot produce breastmilk, or a devoted widowed dad - to effectively tell them that the only way they can keep their baby alive and thriving is bad parenting 'choices' - and, at the foodbanks, akin to them asking for 20 Benson & Hedges.