Everything here is hugely regional, but two answers spring to mind:
1) coriander is frequently sold in unpackaged bunches, typically larger than the packaged ones;
2) it's packaged in plastic because then it can be filled with some inert gas that prolongs spoiling, it's not completely obtuse.
(In the UK for example Waitrose sells it growing reared in Sussex, or packaged grown idk Spain or Monaco or somewhere; Sainsbury's sells it similarly packaged or cut and bunched of undisclosed origin.)