The thing is, we don't know all the facts.
This may be unpopular here, but I'm not sure that a custodial sentence is always the answer. I presume that no driver goes on the road with the intention of killing a cyclist, and what good would a custodial sentence do? Would it bring back the cyclist? No. Would it make other drivers more aware on the road? No. Would be ease the pain of the family? Maybe, but we don't know. We have no way of knowing how the driver is coping. The general option here appears to be that he's (metaphorically) down the pub laughing about it, I very much doubt that's the case.
If someone could show me a direct connection between tougher sentencing for drivers, and a reduction in road traffic deaths, then I may well change my mind, but I doubt there is one.
The driver refused to help the investigation into the death. Not really the behaviour of someone wracked with remorse. In country's that have Presumed Liability, cycling safety rates are vastly better.