They need a flood, so presto, pluck Noah's Flood out of the air. It is a good flood to pick, because it creates a lot of interest. By saying that Noah's Flood was a local flood, do they think they can dismiss the implications of the real global Flood described in the Bible, viz. Even their claim that the Black Sea flood is the basis for flood legends does not make sense. Almost every culture on Earth includes an ancient flood story.
Details vary, but the basic plot is the same.
The classic example is the Babylonian epic of Gilgamesh, but there are flood stories among the ancient Greeks, Romans, Chinese and even the Irish. Although a long stretch of the imagination, it may be possible to envisage these legends originating from the Black Sea flood some 7000 years ago. The latter supposedly entered Australia 40,000 years ago, some 30,000 years before the Black Sea flood. The explanation cannot even account for the flood legends. It makes more sense that all the legends are corrupted memories of the true, world-wide Flood of Noah, as recorded in the Bible.