I'll say what I say to anyone who comes up with some variant of the "Why have these cunts got x years when those cunts got y years?" question. It depends on many factors, including the nature of the offence they've been found guilty of, the sentencing guidelines for that offence, plus any aggravating or mitigating factors. Judges don't just come up with sentences off the tops of their heads.
The rioters haven't been charged with the same offence that the JSO ringleaders were so I'm not sure why you'd even think about comparing the two. But the maximum sentence in the JSO cases was 10 years I believe, so Hallam got half that, and he had a number of previous convictions plus was on bail for a previous offence.