Using a treadmill analogy to understand the mechanics in speed maintenance.
To simplify top speed mechanics, it may help to think of the ground being a treadmill that is moving under you rather than you moving over the ground. If you think of moving over the ground, the leg mechanics may seem more like a reaching and bounding movement. If you think of a treadmill, the importance of foot speed becomes apparent. If the foot is not moving backwards at contact on the treadmill, you should feel the treadmill belt throw your foot backwards. If the foot is moving backwards at the same speed as the treadmill belt, then the belt won’t disturb the stride. It is not this obvious when running on the ground. Your foot will just absorb the impact rather than it being thrown backward.
Since the problem is not as apparent while running on the ground, someone may not be aware of the importance of foot speed at ground contact. They may be doing many things correctly, but they are slowing down every time their foot contacts the ground. Identifying this problem may be difficult because the slower foot speed will prevent them from reaching a higher running speed, whereas the speed of the treadmill can be increased to show whether the foot is slow. If the foot is moving slowly while running, then the running speed can’t increase and the foot won’t be thrown backwards like on the treadmill. I think you always have to be actively accelerating the foot backward, to prevent a passive foot that waits for ground contact.