Man, 'Vidhi ka Vidhan'. What is Vidhi? Lord Brahma, Vidhata. He has the responsibility for writing the fate of a living being/person. And he has to do it according to his 'Sanchita karmas' (Sum total of the person's deeds). So 'Vidhi ka vidhan' has a base and is not totally random. Out of the 'Sanchita karmas', some fructify in one life (Prarabhda karmas).
So this is how it goes. Actions. Their fruits in a person's account of deeds. Big withdrawals, small withdrawals. Big effects, small effects.
How can Lord Shiva interfere in something which is not his field. If it was creation or dstruction of the universe, Lord Shiva can easily do that. He just have to ring his rattle (Damru).