A little off topic but, There is good Adam Ruins Everything about this exactly.
Basically fat provides volume and fullness and also taste. If they reduce fat out of a 32 Oz jar, they have to make up for that 32 Oz and they do it by adding something cheaper (to maintain profit), which is usually sugar, in any form, be it cane sugar or high fructose corn syrup.
That’s why it’s more harmful to health. And sugar causes obesity.
And vegan cakes are Sweet as fuck.