Once you take a probiotic, you will also need to feed those bacteria, otherwise, they will not thrive. Think of it as buying a dog ( your new species in the guts) but giving him chocolate (poisonous) or birds seeds (inadequate) , he will die . You can keep buying dogs week after week, in the same way you can keep bringing new good bacteria to your gut, but not feeding them has no benefit for you.
Gut heath is not about taking a pill bringing new species, but feeding those species, by eating the right food prebiotics, so leeks, witlof, onion, garlic, oats, artichoke, asparagus and banning from your table artificial sweeteners in drinks and food, high fat (crisps and chips), high meat, additives, and so on.