
Speaking to 1Up, Josh Sawyer, project director for Fallout: New Vegas, declared that there was a good reason for the title coming to a complete end when the main story is done.

Obsidian has stated that this is because the player can fundamentally alter the environment at the end, making further playthroughs impossible.

Fallout: New Vegas will not allow players to continue exploring the game's world after the main quest is over, just like Fallout 3 before the Broken Steel downloadable content pack.
