I just looked that up, and I did find some advice that flossing addresses the food issue but not the issue of a bacterial infection not attached to pieces of food, which is probably also obvious. There are suggestions to use a water pick instead of flossing, which dentists have also recommended for a long time, but it's just not as available as string or toothpicks. It's not productive to tell everyone only to use the best possible solution if only 1% will actually do it.

So you have a good point, there are always new things to discover, but this is obvious in a way that's understood and doesn't in any way call into question the legitimacy of dentistry.