Here is the explanation, though it is a bit hard to see from the still shot. Your hands are not leading the clubhead into the ball. This adds loft, contributes to a lower smash factor, less spin and generally makes the ball fly shorter.
The factors for distance boils down to:
- Clubhead speed
- Amount of forward shaft lean at impact
- Smash factor (where you hit the ball on the clubface)
You also got the ball flight, trajectory, ball, club etc., but they don't matter as much as long as they are within normal limits. The speed of the swing itself is probably not an issue, it's more about hitting the ball with the maximum amount of speed. Getting the shaft to lean forward at impact contributes to hitting the ball clean with a downward strike. Hitting the ball on the toe won't make it fly very far. You want to hit the ball as close to center as you can. The amount of forgiveness depends on the clubs you hit.
I used to hit my PW maximum 110 yards, today I hit it 130 yards on a stock shot. My long irons usually flew the same distance, rarely farther than 175 yards. Today I carry my 4 iron 200 yards. I probably swing my arms a bit faster, but the change in distance is primarily a result of hitting the ball clean with a forward leaning shaft. I'm still a bit off center, mostly towards the toe, but my distance is OK because of my impact position.
You got some stuff to work on in your swing, but it's probably best to cover that in your swing thread. I just wanted to give an answer to the specific question in this thread.