The main interest of the RSPCA is in preventing cruelty to animals, which is why they are called that. Fixing up injured wild animals is not actually one o fthe central aims of the organisation. They do do a bit of it, on the side, but other organisations such as St Tiggywinkles are specifically dedicated to wildlife rehabilitation. RSPCA's own advice, on their website, if you have an injured animal is to contact a local vet or a wildlife rehabilitation centre or volunteer. RSPCA do have some such centres, but this is on a "what we can do and where we can do it" basis.

So I find it odd that the vet apparently thought to contact the RSPCA.

When we found a distressed bat on our property, and did not understand the above, not knowing what else to do, we also contacted the RSPCA. They were very helpful, but at no point indicated that it would be possible for them to take it off our hands. Rather they told us what to do ourselves. Which we did. Fortunately this did not involve any medical procedures, so we could.

I would lay into the RSPCA for all sorts of other reasons. But criticising them for failing to do something they don't really claim to do seems a bit much.