Luke arguably grew up in the boondocks.
So did I. Tiny place close to nothing. I still knew world history and the goings on of the current world and so would Luke. He knew about the control of the Empire, sympathized with the plight of the rebellion, ect. He wasn’t cut off from information.
The prequels suck!
Yes, but Star Wars is often like a space “Western”. Luke is the wide eyed kid who’s grown up on the farm and seldom been past the nearest small town. He’s heard stories about the Empire and Rebellion from people in Anchorhead. (The town, not my fellow mod.)
And Owen could have cut certain pages out of the Galactic Encyclopedia. 😉