we do not have the details of the cases so its very hard for anyone (other than the judges and juries involved) to explain any of the sentencing decisions.
maybe it was some matter of foresight e.g. one person committed a crime in the heat of the moment and presumably immediately regretted his action, one person defrauded a company over a long period of time and was then caught rather than came forward... additionally if someone pleads guilty the sentence will be reduced