Ting, ting, ting…
Did you see/hear the ball ringing the vertical lines at constant time intervals? Does it ring a bell in you that the ball is moving forward at a constant speed?
Yup. The force of gravity is the only (significant) force acting on the ball when it was in the air. Since gravity is constant and acts vertically downward, it does not affect the horizontal motion.
That makes projectile motion very easy to analyse. We calculate the vertical and horizontal motion separately. The vertical motion is uniform acceleration motion at g = 9.81 m s-2 (downward), whereas the horizontal motion is constant speed motion.