True that, but it could be both cause and effect. There are reports that gut bacteria can induce depression, which benefits the bacteria because it sends more calorie-rich, highly processed food down the gullet (think ice cream binges when depressed). Not hard to believe that gut bacteria optimized for a particular kind of food could evolve the ability to induce their host to eat that food exclusively. It would have the side-benefit (for the bacteria) of reducing competition from other microbes that aren't optimized for that, by starving them out. Things aren't always just cause or effect, especially in biology.

Maybe. IMHO there is also a microbiome hype train in the recent years. Most of these microbiome studies aren't considering a lot confounding factors. Here is a paper: https://www.cell.com/cell/fulltext/S0092-8674(21)01231-9 that found only very little evidence for association between ASD and gut microbiome.