One simple answer to why... Specific loot.
Apart from the treasure at the end (which can vary), there are bookcases you know about (not in every POI), resources like cobble or cement (also not in every POI), specific devices in surplus (had 2 trucks at an army camp, training equipment and lamp poles outside for f.iron and f.steel), but also surplus of med/ammo/food piles you know about.
Considering it doesn't make that much of a difference in view of found resources, if you know the layout, you can run through "the maze" and only gather best items, to do it again in a few minutes. If you also repeat the poi after a while, it gives enough variety.