For what reasons (legal or practical) are there not (or not more) empirically conditional laws to attempt possible solutions to perceived problems? I'm mainly thinking about in the United States.
It seems true to me that laws could have an easier time being passed if they took a form where we could look at some measure (say, government income), try a suspected solution (say, reduce taxes), and if the desired result occurs (government income increases as is suggested by certain groups based on ideas of the Laffer curve), keep the solution, and if it doesn't, the law automatically phases the "solution" back out. This is as opposed to having long political squabbles over whether some such strategy would be effective or not.
In an extreme case, could there be a law that attempts to set, say, maximum sentence severity based on, say, the violent crime rate? What I have in mind as the most extreme form would be a sort of PID based on specific societal ills and laws known or reasonably suspected to somehow impact those ills.