Because Sasuke decided to join Orochimaru for his PL being higher then anyone in Konoha
His PL is why Konoha can't easily kill him in Shippuden, nor can the Akatsuki, who he technically competes with in early part 2 etc.
Kisame is not receiving the same treatment, he certainly wasn't a child prodigy being groomed to be a Kage lol, and the strongest in the Akatsuki are pretty consistently the most plot relevant.
Plus, Orochimaru has:
Poison
Swordsmanship for cqc
his Snakes can save him from the water
Regen
If you include Edo Tensei, that's kind of a big deal, but unfair, I guess?