We know, more or less, how they're made and what they're made of, to the degree that even a child can make a cake without much problem.

We have overwhelming evidence of not just the existence of cakes, but also the various recipes for the multitude of types of cakes that exist.

It's a process we can not only observe, but in which we can also participate.

Conversely, for the universe, we have only the existence of this one universe, with a finite scope of observation. We have exponentially less evidence showing how the universe came into existence than we have for any one of the innumerable cakes that have existed.

It's not even an apples to oranges comparison, it's birthday cakes to a universe.