For that image? What's up with the moon and why is it so close? Is it inhabited and indeed, does its proximity effect the planet in some way beyond simple tidal forces? What's with the low cloud cover? Is the atmosphere unusually thin? Are those lakes of water, or so sort other liquid? If it's not water, is it dangerous to go swimming? Is it even liquid, it could be frozen from the looks of it. Why do things looks sort of hazy? What's up with those blue/purple bushes? If that is the local star to the left of the moon, is it flashing or pulsing for some reason and if so why? Why is the sky that color? Why is there no vegetation, other than those blue bushes and what appears to be grass? There are no trees or any other kind of plants anywhere. Are there any animals in the vicinity? Spock, have we been here before? This matte painting looks like the planet we visited a few weeks ago.
I'm kidding, sort of. More specifically though, I was referring to the previously comment about stumbling upon a planet that appeared to have no moons and orbit no star. Sure, they can get away with not explaining why the planet appears to exist on it's own, but some comment about other planetary bodies in the system and the star they're orbiting isn't too much to ask for.
It only takes a moment to include a throwaway line about the rest of the star system. And my point was that if you're going to go to the trouble of doing something, than why not go just a bit further and get the details right. Or at the very least include some details that sound right, even if you make them up. The existence of the Tech Manual suggest there are plenty of people who care about such details, even if they never make it into the show or add any great depth to the story.
I'm not really sure why you assume these planets are "just there".
Many times we join the ship when it is already orbiting a planet. Other times we might see a planet gradually growing larger on the viewscreen. The ship's sensors are centered around showing their destination, the planet itself.
You can easily imagine Spock's science station picking up all of the other relevant astronomical details and forwarding them to anybody else who needs to know if you like.
Honestly I think you are in the minority in wanting more of those types of details...which is fine! We all like different aspects of the show, but for most viewers I really don't think it would add much, and might even be dull or annoying to others. It simply wasn't the focus of the show to delve into such minutiae.