If you luck out of a game that the way it was played would have resulted in you losing 95/100 times save a pick six or something like that, it still hits you with a "loss" - you played bad.

Conversely if you outgained them by 450 yards but somehow lost 14-13 you would get a "win"

So there's a huge overlap but it's not strictly W/L. It's playing good or bad and playing good usually = wins