Because awful stores like Gamestop and the like are using their commercial influence to coerce publishers into pushing back digital release dates to match the physical store release dates, so they can remain competitive.
This is why I never buy boxed copies anymore, I can't support this bs that only hurts the games industry and games sales as a whole. As the topic starter said, torrents will run wild, while if it was released worldwide at the same hour, people would get sick of waiting and just buy it instead. (the ones that are capable of pirating it i mean)
There really is no good outcome of it, except for Gamestop etc.
Cheers for them, hipp hipp hurrah.... Bastards.