I kinda get it where pork in soap recipe comes from, but still, meat is not fat. And one needs the later to make soap. Fat o-o-or... wax. And we do have wax in vanilla minecraft.
Also not sure if this is possible, but if it is, can soap recipe use fats from other mods? Namely Occultism, Quark and Hexerei all add fat drops to animals, often resulting in inventory clutter (and Occultism specifically is the biggest offender of the three).
Changing the recipe to use vanilla wax \ modded animal fat would greatly improve it in both immersiveness and realism.