What's the meaning of "bake into" in this context

It means that the current results include, take into account or are based on past drivers.

Have any more context? It's not clear (to me, anyway) exactly what is being called "past drivers of margin expansion."

I assume it's something like this: Say you want to bake a pie. If you want an apple pie, you put apples in before you bake it. Cherries if you want cherry pie.

Once the pie comes out, you can't change it now. The ingredients are "baked in."