Comment by Retric
Tradeoffs. Physical land under the airport is lost either way, but land near the old airport becomes more useful where the river itself couldn’t have buildings in either situation. Thus moving it near a river or other large body of water is a long term net gain.
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.
To be fair to this specific airport, the industrial area South of the airport is almost entirely UPS Airlines facilities. The safety hazard posed by the UPS Airlines flight crash was primarily to UPS Airlines warehouses and warehouse workers. They made their own tradeoffs in this case of what they placed close to their own runways (including apparently they had a fuel recycling plant not far from the crash line that made firefighting more complicated). Sure it's still very different from a large body of water, but it's also certainly not like the land was entirely a general usage industrial area either.
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.