Well, the reasons KC won last year are a bit more of a coin flip, I think... Remember that Seattle was the better team on the field last year, so the match result was more of an upset, while this year KC was the better team on the field so them winning was easier to see and understand.
I don't know, as much as I hate to say it, Elli Reed fell and, as a result, KC got a goal. True, ARod got open in front of the goal, but that could have been more a matter of poor marking, so there's probably another defender to bear some of the responsibility. It probably wasn't apparent on the broadcast after the game, but Elli was absolutely devastated. This simply was one of those games where one error led to the result. Think of it this way: Elli Reed doesn't fall, Rapinoe's shot is two inches to the right, the analysis doesn't work.
Elli just entered the game as well, an emergency substitute for Kendall Fletcher. She was barely warmed up. Unfortunate situation.