Because I was making the point that prison doesn't always solve anything. Whether he goes to prison for 10, 5 or 2.5 years doesn't really change anything. It's not going to reform him and he'll be back on the street regardless.
All an increased sentence does is make people say it's fair. But that's all it achieves.
Pistorius' punishment of having his career ruined, income streams ended for life, living knowing he's a killer, living knowing everyone thinks he's a killer, is worse than him spending a few more years in prison.
So his sentence is just a number. It's not going to change him and him being in prison for a few more years isn't going to make the world a safer place IMO.
So I'm just pointing out that yes he has got a light sentence, but a longer sentence doesn't really change anything other than make you or I think it's fair.