It would be absurd to walk into a kosher restaurant and expect pork to be available.
I wonder if this question is attempting to falsely lead to "So why would you expect a Christian to bake cakes for gay weddings?"
IF SO... The error is this:
Kosher restaurants SUPPLY "kosher food". Anyone would reasonably expect to walk into a kosher restaurant, ask for, receive, pay and walk out with kosher food. It would be ABSURD to walk into a kosher restaurant and demand pork. Cry foul when pork is not even in the building.
Wedding cake bakeries SUPPLY decorated cakes. Anyone would reasonably expect to walk into a bakery who bakes then decorates wedding cakes, order a wedding cake to specs, receive, pay for, and walk out with said cake. It would be ABSURD to walk into a baker and expect a souffle. Demand a souffle. And cry foul when the bakery cannot supply a souffle.
If that was not your intent, then my apologies.