Well this is just speculative but maybe a portion of unsuccesful attempts goes towards decay of some sort.
Otherwise crafting contributes to decay via the items that are used after they are crafted. Ore amps are a good example of items that have high decay and are used quite frequently.
Pretty much everything leads to decay if you think about it. The "no deposit" sweat gatherer sells his sweat which is refined (decay) and made into ME which is used in MF which decays. More than likely the peds made from sweat will be spent on hunting or mining adding more to the decay bucket.
Its clear in some activities how much goes into the
MA decay bucket and sort of a grey area in other activities like Melee and the such. From our standpoint crafting looks like a 0% decay activity and melee a 100% decay(no ammo) activity while portions of both might be recycled and some going to the
MA decay bucket. Only
MA knows for sure though.
IMO I think
MA takes a little here and a little there some we can see and some we cannot and at the end of the day the remove a tidy sum of peds out of
EU.