But also there's a lot of urban and suburban development you'd have to displace to even consider moving the airport near the Ohio River for most miles both up and down stream of Louisville.
As to a crash, ditching into an industrial area isn’t significantly worse for the passengers than ditching into a set of rapids, but the rapids are far better for the general public.
Had the crash happened in a different direction there might be other complaints, sure, but even airports with large bodies of water neighboring them only generally neighbor a side or two.