In that model and imbalance of resources, having statue of limitations in place alleviates the need for defendents to, for example, keep records of their actions and reasoning for 30+ years. How would you navigate being charged for tax evasion from 35 years ago, for example?
EDIT: to be clear, I don't think this is necessarily a precise defense of statuetes of limitations specifically, just a "well they're not a bad idea" sort of defense