Coaching & front office negligence is the issue, still.
Clock mismanagement (letting 40 seconds run off the clock before first timeout used, going for a TD instead of going for a first down to bleed more clock before trying the tying FG or for a game winning TD).
Secondary can't cover, and they still keep playing the same guys every week. We spend draft assets on defense and it never seems to get better.
Most WRs can't separate either.