Why is LB allowed to keep her chains on you while she becomes untargetable?

seems like little to no counter-play for that and it seems a bit unfair. What I mean is if you are hitting and she casts her chains on you then disappears because passive she can still keep the chains on you but is not targetable for the purpose of responding to her attack. She will reappear but by that time you are rooted and more than llikely out of her range. I don't mean for this post to sound whiney or complainish but I am curious as to why she is allowed to do that (kind of like being allowed to sleep at the TOP of his troll pole when hit with a sleepytime bubble; lil' bastard should fall.)