It’s completely understandable how a “transplant” could reintroduce necessary bacteria into a colon where it had been destroyed. Agreeing with other posters here, C. Difficile is gawd-awful.
It’s not as easy as eating a source of the necessary bugs, as the stomach will kill them with acid before they get to the gut.
There’s one thing that will kill C. Difficile and it’s oral vancomycin. But it is not used except in extremis because it is also the last chance antibiotic for a number of bacteria that are on the verge of developing vancomycin resistance. And after killing the C. Difficile now what? You still have the problem of putting the good bacteria back.