I'll tell you - because of the issue of "temporal jurisdiction".
@Shamain, do you know when the ICC came into existence? It was in 2002. The principle of temporal jurisdiction (and a few other jurisdictions) dictates the admissibility of complaints to the ICC. Temporal jurisdiction means that only crimes committed on or after 1 July 2002 can be heard by the ICC. And that is only one of many reasons.
In short - the ICC did not exist when the Pak army genocided Bengalis, and the ICC cannot retrospectively admit cases - if so, India and Pakistan would be filing hundreds of cases against Britain, Iran, Afghanistan, Turkey etc for every war crime in history.
[/B]Secularism is not a religion[/B].
Pakistan lost more than half its country (by population) in 1971. That is, in 1972 there were less than half as many Pakistanis as there were in 1970. You can check the census figures if you don't believe me.