Because there's not really any indication on when Downpour takes place. Personally, I've searched high and low, and calculated the possible years for the calendars in the game. The calendar's are inconsistent, and there's no official word on when it takes place.
I gathered all the dates from Downpour I could find there, however, a lot of them are contradictory, and because I want an accurate timeline, I don't want to be biased which is why there's no real date for Downpour yet.
If you want a legit answer, I guess you'll just ask the apparent three writers of Downpour: Tom Waltz, Tomm Hulett and Devin Shatsky.