Any time a decision is made, it's up to the whims of somebody. What you're saying wouldn't make sense even if we had technical means to deterministically decide everything.
There are very few punishments in Western democracies not subject to some level of judgement call. Until we've got AIs, questions like "was this deliberate" and "how much non-monetary harm was caused" will require a human (or group of them) to make a call.
The law says "up to [that much of a fine]", not "exactly [that much of a fine]".