Video editing apps allow you to place more than one clip on a layer. However, AE, being at its root a compositing app, thinks more “vertical” rather than “horizontal”. As a result we have “one clip, one layer”.
If you want, you could apply time remapping to the clip. That will give you two keyframes: start and end. If you copy those keyframes then paste them somewhere else on the same layer, the same clip will start and play again. You see? So every time the clip plays, you see the start and end keyframe.
Does that make sense?