Because the increase would create more of a deterrent and improve society .
I think that's the main issue. Tougher sentencing doesn't tend to reduce incidence of a crime, or at least it's rare that it does. I appreciate that it's counterintuitive.
However, increased likelihood to be caught for a crime does reduce incidence.
Yup. People don't consider the sentence, just how likely they think they are to get away with it. Motorists know they can speed in most places with a very low chance of getting caught. etc.
My memory is a bit hazy on this but I think in relatively recenty years there was an increase in sentences for assaults on emergency service workers but despite this the number of assaults increased.
I think that's the main issue. Tougher sentencing doesn't tend to reduce incidence of a crime, or at least it's rare that it does. I appreciate that it's counterintuitive.
However, increased likelihood to be caught for a crime does reduce incidence.