Because what happens in a singly-linked list -- this is trying to remove an existing entry from a list -- and there's a difference between if it's the first entry or whether it's an entry in the middle.
Sest lihtahelaga on nii, et kui sellest püütakse eemaldada üht sisendit, ja on suur vahe, kas see on esimene sisend või on see sisend ahela keskel.