It's because it's a very new field. Few people would have ever thought diseases of the 'mind' could be related to the gut biome, so people are still actively researching exactly what is causing what. It's not because there's any question of whether this is an issue at all.

This is also an extremely important discovery, but it will have profound implications on modern health and diets. Everything from glyphosate to fake sugars has been argued to be harmless because we thought that they were largely inert. In reality they are having substantial impacts on the gut biome - the potential implications of this cannot be overstated, and so shooting wild and fast would be poorly advised.