Looking at you, No Man's Sky

Within the TMZ, thirty mile zone, because union rules say you have to pay transportation time for workers above that limit.

Oh man, in general, people be raving about aliens, but never give two looks to the ants in their garden. Or you know, the entirety of Australia. Or the deep sea. We have so much life that's alien buzzing around us. Hell, we even have the Scottish – humanoids that speak an entirely cryptic language. It's so much more compelling story-telling, too, if they don't arrive here in a spaceship, but rather have been living among us all this time.

Some Sci-Fi planet types are reasonable.

The Kepler program found a lot of exoplanets and has categorized them generally as Hot Jupiters, Cold Gas Giants, Ocean Worlds & Ice Giants, Rocky Planets and Lava Worlds.

If you ignore the gas giants because there's no surface to land on, rocky planets (and maybe desert planets) would be extremely common. Water or ice planets would also be incredibly common. And, if you're really unlucky, you might end up on a lava planet -- one that's small and very close to its sun.

What wouldn't be common are things like an entire planet that's a swamp, or an entire planet that's a forest of Earth-style trees. I'm sure it's entirely possible that on some planet there's a life-form that becomes the dominant form and that looks vaguely like Earth-style trees, but not the kind you see on a typical SciFi show filmed near Vancouver.

My favorite is how there is only ever one city and like 10,000 people on any planet.

Oh he went to this planet? Well, lets just go to the market, he's bound to turn up at some point.

Star Wars even have a city covering an entire planet

Yes, they copied it from Foundation. Trantor has a perfectly fine reason for being the way it is, that would apply to Corusant too.

That is, if physics actually allowed them to be that way. Apparently Asimov didn't run the numbers on that one.

Dr Who: Every planet is a disused quarry.

In Foundation, Asimov suggests that spaceships start running on coal power, after civilization collapses so far that people forget how to build nuclear engines. He was always more of a Big Ideas Guy than a Fine Details Guy.

They are more subtle, but they are there. And it does have an atmosphere. It's substantial enough that communication to the surface can be lost for months due to planet-spanning dust storms. Yes, it's only 1% the pressure of Earth's at the surface, but that's enough, especially when you allow forces to act over geological time scales.

And yes, they can be as varied as those on Earth. Life doesn't actually increase the biome variety as much as you think it does. The kind of life you get in any given biome on Earth is a direct function of the geology and climate in the area. Input a given altitude, rainfall, temperature, and soil conditions, and you'll get a similar biome anywhere on Earth. Yes, there are different individual species in the rain forests of South America vs the rain forests of Africa, but they're both rain forests. They work as biomes in similar ways. Wherever the local climate and geology support rain forests, rain forests sprout up. The only exception is isolated islands that can't be reached by certain species.

This is why Mars can have the same biome diversity as Earth. The living components of Earth's biomes are a direct mapping to the nonliving components. Earth's living biomes are no more diverse than the underlying geology and climate.

And this is before we even consider Martian life forms, which almost certainly exist. We know of bacteria that exist deep in the Earth's crust that, if you transported them to deep under the Martian surface, would be able to survive and thrive just fine with zero modification. We know Mars used to have vast oceans and all the ingredients necessary to get life started. And we've seen numerous bits of circumstantial evidence of bacterial life present in some capacity on Mars today. While scientists are loathe to affirmatively proclaim life on Mars. The extant existence of bacterial life on Mars today really isn't that an unusual claim. If life could get started on Earth, there's no reason to believe it couldn't have started on Mars. And that's before you consider pansperia. If nothing else, we know life can comfortably exist deep in the planet's crust. And who knows how such life might affect conditions on the surface.

If you ignore the gas giants because there’s no surface to land on

Hey now. You can land on the surface of Jupiter if you're dense enough.

Honestly, by the numbers, Earth is mostly an ocean/forest planet with some desert. Desert and ice planets are believable, too, given those are more temperature-based, and city planets seem like they'd be inevitable in a sci-fi setting just due to population sizes.

Yeah, the holocene is a weirdly varied time period for climates. Grasslands and similar ecosystems are pretty new geologically.

Wait, wasn't it a metaphor for "some nuclear reactor so rudimentary that they could as well use steam engines"? I really don't remember it well.

Anyway, he's famous for running the numbers for some things. But yeah, he absolutely didn't do it for all things.

Depending on the setting, that could make a lot of sense. Imagine a planet settled entirely by the descendants of a single expedition. That planet wouldn't be a complete cultural monolith; not everyone would be identical. But an entire planet with the cultural diversity of a small place like Iceland really isn't unreasonable. If it's a species' home world, that makes less sense.

Or, a really dark bit of head canon? Every time you find an alien species that lives on its home world and has a single culture? Inevitably this means a cultural evolutionary bottleneck existed in the planet's past. If it's not a colony planet, then something else must have caused that bottleneck.

My head canon? Any planet like that is one where an alien Hitler won. When you encounter a planet like that, it means that some time in the last thousand years or so of that planet, a Hitler-like figure came to power and achieved global hegemony. They decided that there was one and only one right way to live. Everyone was either forcibly converted to that lifestyle or done away with.

Mars has no biomes because Mars has no known life. You can't skip the "bio" part of the word.

"This is all one castle."

I think you're vastly underestimating how quickly culture deviates and develops. A planetary mono-culture would require every person to grow up in exactly the same circumstances. No stratification from class or gender or sex or age or ethnicity. No varying seasons or biomes or climates. Exposed to all the same media at exactly the same time, and all with the same intelligence and personality and ability to interpret it.

In short, the only time a mono-culture makes even a tiny bit of sense is when it's a hivemind. (Or mind-control but that's pretty much the same thing)