Something about it tastes... off. It's not sweet enough, for one. You've considered dusting it in powdered sugar - it's a reliable baker's trick, after all. But you don't think that would even salvage it.
It just doesn't give that feeling of earnest success that well-made food normally does. Even with as terribly as the red velvet and chocolate cakes went... you hated this most of all.
Maybe it's just cakes in general that you're fucking up.