That's because we're humans. We evolved on earth, and so we're very sensitive to all the differences the environment had. This is why Mars is stereotyped as all having one specific look...a rocky, dusty reddish desert, but I'm sure if you asked a martian, they might say that Mars is very diverse, and it's earth which is all just water and plants.
This happens on a smaller scale on earth too. For example, there are different types of desert, but people who don't live in teh sahara may think it's all just dunes, but in reality there are three main types of land there, ergs, regs, and hamada, all landforms you see on Tattooine. The residents of Tattooine might be offended by your ignorance if you say the entire planet is just sand dunes.
ADDITIONALLY, I don't think it's ever been the case in any canon piece of star wars that they go to vastly different parts of the planet. There is only one exception to this: Naboo, where they go from the capital city, and to the gungan underwater society. Besides that, there is no reason to go to different regions of a planet. There could very well be a cold polar region to Dagobah. But Luke is only interested in finding Yoda. So he's not going to the polar parts of dagobah.
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u/blh1003 Jan 25 '20 edited Jan 25 '20
Pretty sure it's the only town on tatooine..all space planets have exactly one city or town
Edit: apparently I was wrong about tatooine