We have around 500 species of bacteria living in our guts. Yogurt uses only 2 or 3 species of bacteria. So it's not surprising that eating yogurt didn't change various aspects of behavior.

Great point. We have, as far as I know, little direct information about how effective the fecal transplants mentioned above really could be (at least in humans) in situations that aren't last resort.

I attribute this ignorance to the (important and reasonable but perhaps exaggerated) desire to protect us from risks of unknown treatments. The unfortunate consequences are ignorance and an interest in "alternative therapies" (which we could generously characterize overall as experimentation by non-professionals without proper institutional support).

Edit: I think I see another discussion post forming here in my head, but I'm getting a bit carried away.