Even if it was cheaper to purchase and maintain, it wouldn't be more efficient, because money spent is not necessarily the measure of the efficiency of the just

Even if it was cheaper to purchase and maintain, it wouldn't be more efficient, because money spent is not necessarily the measure of the efficiency of the justice system. That could be, for example, lower criminality. If a system fails to jail enough criminals to do that, even if it's cheap, it's not working. And also, false positives (e.g. jailed innocent people) are especially troubling and can be very expensive in a justice system.