That one economics paper, as an example, could have made one seemingly innocuous assumption that might be overlooked by later work.
Let's say a paper that relies on the preprint take that assumption for granted. And then another paper references that one. And again. And again.
Then the fifth paper gets adopted by a government in some esoteric policy, which causes their economy to implode.
May not be necessary to just publish "stuff", but it is necessary to mitigate against the dangers of invalid assumptions.