science fiction genre - Why aren't alien planets as varied in climate as the Earth?

The Earth in all of its varieties has wide ranging climates. At the top level it has tropical, dry, temperate, continental, and polar climates. And yet often the planets depicted in science fiction are often single climate planets.

• The forest moon of Endor


• The desert planet of Dune


• The desert planet of Tatooine


• The desert planet of Vulcan


• The outer planets in Firefly all appeared to be mostly desert (supiciously like Calfornia desert).


• The inner planets in Firefly were all temperate or tropical.



• The icy Breen homeworld


• The icy Andorian homeworld


• The icy Frost Giant planet

I'm not suggesting there are no Earth-like planets in science fiction, but it feels like it is less common than it should be. Considering the only planet we have as an example is our own, it seems like planets should be just as varied in the cosmos.

Answer

This is known on tvtropes as the Single Biome Planet trope:

Planets in outer space will often be defined by a single setting. It doesn't matter if the events of the story only take place in on a small portion of the planet — we are still told the entire planet has one climate; specifically, the same climate as where the story takes place. Very rarely does any planet have the same level of environmental diversity as Earth, despite being as large and having a normal orbit. An ecological equivalent to the Planet of Hats.

See the link for a more complete description and a pretty long list of examples. It also discusses when single biome planets can be justified.

Personally I am often annoyed by the frequent occurrence of this trope in mainstream SF and Fantasy (although the latter also often succumbs to the opposite, Patchwork maps). It can make an entire world flat, uninspiring and implausible, and I would advise any aspiring SF writer to avoid this at all cost.