In the foreword in this recipe booklet from the 1920s it says:
Be lavish with raisins. It is justiﬁed by dietetic worth. They furnish 1560 units of energizing nutriment per pound, more energy than eggs, milk, meat or ﬁsh. They are 76 per cent pure fruit sugar in practically pre-digested form so their good is almost immediately assimilated.
They furnish food iron and valuable organic salts. Put raisins in oatmeal and in cookies, cakes and breads. Serve bread puddings, boiled rice and breakfast cereals with raisins. They improve sweet potatoes, candied or mashed. Raisins make plain foods delicious—be lavish with them.
Oh, and yes, Sun Maid pack and sell raisins 😉