This is actually a super easy way to identify when you are looking at a planet in the night sky. Also, all the planets are in one plane, so you usually identify other planets in the sky by looking in the same axis.

Stars are so very, very far away that they are effectively point-sized spots of light, which can be very easily influenced by random atmospheric disruptions.

Planets are much closer to us, so they appear to be disks with an apperent diameter. Since they appear much larger from our perspective, they are less liable to ‘twinkle’ due to atmospheric disruptions.