All very interesting - there are things called impact assessments which are used for legislation to predict and justify impact - the Westminster Parliament does not insist on impact assessments for Bills - statutory instruments normally have them - the devolved legislatures normally have them - they carry from almost the kind of specific modelling you are talking about to something more generic and less helpful from your perspective.

Interesting point about blame - but of course they also want credit ... Impact assessments carry risk for the reason you give, but also possibility of credit.