Probably it's just how the math works out. The atoms emit in all directions, however the waves traveling in all the other non-correct (according to reflections and refraction laws) directions cancel each other out, and only the ones with the new correct direction are still there / visible.
Thanks for correcting me and thanks for the link. But what have I been talking about so far? I don't understand.
Also I just watched this video I'd recommend that explains the idea: https://www.youtube.com/watch?v=NumSE2LvSmQ
