The Broncos have scored the 2nd fewest points in the entire NFL. Yes, even the lowly Cleveland Browns have outscored the Broncos. The problems with the offense are many, but there are a few glaring ones: 

1) Extremely poor coaching. While he's not calling the plays on offense, this is on Vance Joseph first, then Mike McCoy. 

2) Lack of talent at QB. This has been evident for 3 years. Siemian is not a quality starting QB, and is a mediocre backup at best. That said, he is still the best they have on the team, which is pitiful. This is on Elway.

3) Turnovers. The players have nobody but themselves to blame here. They have turned the ball over with regularity, oftentimes at crucial junctures. You don't deserve to win when you play so poorly. 

The Chiefs are going to embarrass the Broncos tonight, then it's off to Philadelphia to be embarrassed again and then back home for another embarrassing drubbing at the hands of the Patriots, at which point the Broncos will be sitting at 3-6.