Why is this a bad thing? They’re getting a well-liked, reliable fast food option
Because I don't think chain fast food belongs inside most* theme parks.
Even if it is just CFA served inside of an appropriately themed restaurant exterior, I believe themed culinary is an integral part of the larger theme park experience. Certain sacrifices must be made to make dining accessible to more pedestrian palettes (read: offering burgers/pizza/chicken fingers somewhere in the park), but I believe actual culinary investment should take place on the themed dining front.
If Three Broomsticks at Universal started serving Chick-fil-A, people would be (rightly) confused and angry. The same principles should apply to Busch Gardens parks in my opinion.
Theme parks sell immersion and escapism. If I'm strolling around 18th century Europe and stumble upon a Chick-fil-A, something has gone terribly wrong.
* Chick-fil-A in a theoretical modern, GA-themed, park area? Perfect. Chick-fil-A in an area of a park themed to a chicken farm? Clever AF. There are themes that could reasonably house a Chick-fil-A inside a theme park—none of those themes currently exist at a SEAS park though.