I think this problem is actually a physical problem, not a statistical or philosophical problem. And I think you’ll get better answers than mine if you post this problem on Physics SE.
All pro golfers, and all golfers who have a good form alike, always follow through after hitting the ball because that’s both the most effective way and the least injury-prone way to hit the ball. So, they are taught and trained to do so – the practice of following-through is intentional and does not happen in them by haphazardly by chance. That’s why the chance that all pro golfers do the follow through approaches 100 per cent.
The most effective way to hit the ball.
The collision between the golf club and the golf ball is not a collision between two perfectly rigid bodies. Unlike the collision between two perfectly rigid billiard balls when the contact time between the two balls is virtually negligible and the effects from the incoming ball ceases immediately after it hits the outgoing ball (i.e., no follow-through effects at all), the actual contact time between the golf club and the golf ball lasts some milliseconds and the effects from the golf club depends on the time it remains in contact with the ball.
Follow-Through in Sports
In sports where rackets and bats are used, like tennis, cricket, squash, badminton and baseball, the hitter is often encouraged to follow-through when striking the ball. High speed films of the collisions between bats/rackets and balls have shown that following through increases the time over which the collision between the racket/bat and ball occurs. This increase in the time of the collision causes an increase in the velocity change of the ball. This means that a hitter can cause the ball to leave the racket/bat faster by following through. In these sports, returning the ball with a higher velocity often increases the chances of success.”
So, if a follow-through is not executed and the golf club stops at the moment it impacts the ball, then the time of contact between them will be less than if a follow-through is executed. As a result, the energy transferred to and the control of direction of movement of the ball will be less effective. Thus, to hit the ball most effectively, the hitter must do a follow-through after he hits the ball.
The least injury-prone way to hit the ball.
One may ask “why not stop the golf club immediately after the above mini-follow through is done and the ball has actually separated and moved away from the club, that is, why do the whole-range follow-through?”.
The answer is
Physiologically, it’s impossible to do just the mini-follow through. To stop swinging the golf club immediately after the ball has separated from the club, we must know when that moment occurs. But it takes time for the physical signal of that separation to travel down the golf club to the hand to the spinal cord and finally to the brain of the golfer, and it also takes time for signal processing and sending back signals to the involved muscles to stop swinging the club. So, physiologically it’s impossible to halt the club swing immediately after the ball has left the club. However, it’s possible to halt the club swing some milliseconds after the ball has left the club, but this is a dangerous thing to do.
Physically, when one swings a golf club, momenta are imparted to not only the golf club but also several parts of the body – the arms, the body, the hips, the legs, etc. – and the muscles of these parts are contracting, some of them quite strongly. The more energetic the swing, the more momenta are imparted and the more strongly the muscles contract. If one tries to stop this whole complex, energetic movement and muscle contraction suddenly, injuries can occur to these parts. So, to avoid these potential injuries, one must follow through the whole range and let the momenta dissipate and the muscles relax gradually.
… upper torso rotation during follow-through phase of the golf swing likely contributes to power generation and to a smooth swing pattern that may prevent injury, and thus may warrant specific training strategies. 
The follow-through is important in slowing the body parts down over a longer period of time, absorbing the forces produced and helping to prevent injuries.
- To stop swinging the golf club at the moment it hits the ball is not an effective way to hit the ball.
- To stop swinging the golf club at the moment the ball departs the golf club is physiologically impossible.
- To stop swinging the golf club some milliseconds after the ball departs the golf club is possible but injury-prone.
Therefore, all golfers are taught and trained to do the complete follow-through. Because the advice works, this results in the majority of golfers, especially pro golfers, do the complete follow-through, leaving only few golfers, if any, not doing the complete follow-through. That’s why the chance that golfers, and even more so for pro-golfers, do the complete follow-through approaches 100 percent.
12.13 Physics in action Siyavula textbooks: Grade 11 Physical Science.
Katherine M. Steele, Eugene Y. Roh, Gordhan Mahtani, David W. Meister, Amy L. Ladd, and Jessica Rose. Golf Swing Rotational Velocity: The Essential Follow-Through. Ann Rehabil Med. 2018 Oct; 42(5): 713–721.
Skill Analysis & Coaching GymSports. New Zealand.