Story-based reason for the game's premise?

Saw someone claiming it doesn't make sense for the violence between Raiders to be almost entirely exclusive to the surface and it got me thinking...

Any number of people that emerge from a return point will have no chance of getting past Security forces. It could be because they'd be outnumbered. Or outmatched by structuring, structural integrity and weaponry that make the checkpoints fail-proof against anything they could find Topside. Security could very well be equivalent to a real-life military force with how much time has passed in the story.

On top of all that, every person in Speranza wants a secure place to stay. Where they don't have to suffer the fatigue of attrition.

True anarchists, masochists and actors of that sort would've run their course early on. The people who both wanted to survive the most and had the capabilities to do so took the time to develop an almost perfect system that stood the test of time. Shani's a good example, one of the likely many diligent minds working to prevent whatever or whoever from harming what they have going with Speranza