The batch size limit helps prevent the player from carelessly crafting items that would take several days to complete.
Some of the problem is how crafting time scales with batch size. After performing a quick (not full) butchery of one goat, I had so many units of liver (36 or so, I think) that a full 20-unit batch took some 11 hours to complete, during which my character became quite hungry and thirsty. And I still had more to cook. This was one damned liver from one damned goat, mind you.
It’d be nice if an interrupted crafting session would yield partial results. If a single unit takes 30 minutes and each additional unit adds 5 minutes, then stopping after 40 minutes could yield 3 items (and consume the components for those three), even if you were trying to produce a batch of 10. Batches larger than 20 would be less problematic then, since you could stop to eat/drink/sleep or defend yourself and still not have completely wasted hours of your time. Want to craft 10 but only have time for 3? Just finish the rest later as a batch of 7, even if it takes the additional 25 minutes for the first item in the second batch.