You microbiome is more akin to a forest than a farm. You can't just plant potatoes (or whatever) and assume that it will get balanced. Sometimes things like this do help, but sometimes they don't. Fertilizer makes plants grow, but it can have unintended consequences. (For example, runoff leading to bacterial blooms in a watershed.) The gut is an ecology, hence the difficulty of determining one-size-fits all fixes to a complex ecosystem.
My suggestion was for a cheap and easy hack that is likely to benefit a majority of the population. Obviously the best way is to have a well-rounded diet and get all nutrition that way but we know that can be challenging for many.