This post may seem a tad untasteful, but it serves a purpose, so please read on.
Consider what happens when living beings excrete solid waste, the poop ends up in nature (hopefully not too near a stream), and does not stay there permanently, instead it gets broken down into fertilizer by microbes.
Something develops (through evolution) so: what’s useless for one being, gets consumed by something that needs the waste to survive, turning that waste into stuff useful for the excreting beings.
Something similar happens when for instance scrap metal merchants relieve human setlements of their old cutlery, old cars/bikes, discarded buckets etc. They recycle them into metal used for making new buckets/cutlery etc.
So because the waste products can be used for profit by entepreneurs to relieve others from their waste, turning the waste into useful products for the first group. So, it’s a simple simile for natural processes.
Once again, where comunism/socialism are unnatural, capitalism isn’t an “-ism”, it’s what people do when you leave them alone.