Many have answered about storage costs. Easy way to think about it might be a grocery store.
You hear about a sale on cereal for $0.01 a box. Great deal but then you find out that you can't walk there, you can only take Lyft/Uber and it costs $100 each way to get to the store. So in reality its not as good a deal as it sounds.
The part about depending on only semi-reliable third parties for your logistics, or the part about the supply chain costs being 1000x your material cost?
You hear about a sale on cereal for $0.01 a box. Great deal but then you find out that you can't walk there, you can only take Lyft/Uber and it costs $100 each way to get to the store. So in reality its not as good a deal as it sounds.