Why are Stars Flashing ...?
The star is so far away that it resembles a point. The star's light is deflected by a layer of dust and water drops as it approaches the earth. Each layer is different - its thickness is concentrated. The more concentrated, the sharper the light is deflected. If the dust is silent, then the star will look like a dot light. As the dust moves, the starlight sometimes appears sometimes.
Why the planet does not flicker ...?
The planet looks great (close to the earth). The twinkling is not caught by the eye.