Why does Nasus have a lifesteal passive?

He can't be bullied in lane with the new mastery now. I take him to half health and he just q's and I become half health and he gets all his health back pre 6. Laning against Nasus is a lost lane in itself. You can't stop him from farming. The only way to stop nasus early is for mid and jungle to camp him. how is that an ideal strategy? Saying I need other laners help means there is something seriously wrong with that champion.