That statement is a little over-exaggerated, you don't actually know that, they haven't travelled to the poles of the planets so you're really just assuming.
What is true is that the planets climates aren't as diverse as Earths, but it's acceptable to have a desert planet or an ice planet, which is what our planet would be like if the average temperature was 10 or 20 degrees higher or lower.
I'm sure that planets like Naboo and Yavin differ in climate in places, Mustafar is like earth billions of years ago.
Some planets just aren't as diverse as ours, perhaps not as evolved as ours, like Mustafar or they are even more evolved than ours like Tatooine or Hoth.
So what you said is a bit exaggerated, not every planet, and probably not the same at the poles, but it's ok for them to be the same climate in most cases.
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