that sentence is not exist ... i think something wrong when you translate.

In your original text I will add '그' ' 그것들이 굉장히 큰 자양분이 되다' 것들 can be translated into things but without '그' it sounds like not a complete word. They have become very big nutrient. = 그것들, 되다 , 매우, 큰, 자양분. as you know nutrient is helping something grow bigger and better.. So it means ' they have become a stepping stone' or 'they have supported (something) tremendously'