Because it wouldn't involve handling live animals, could be significantly more automated, would not need as much real estate, would eliminate wastage of the par

Because it wouldn't involve handling live animals, could be significantly more automated, would not need as much real estate, would eliminate wastage of the parts we don't really consume, could be done at larger scales in a more centralized way where energy is cheaper, the stages could be pipelined with processing/packing/etc happening at the same place. I'm sure there are a dozen other reasons I didn't immediately think of.