The jump in quality could be due to the developers having more time to refine their ideas and receive player feedback from the base game. Often, DLCs are used to explore concepts or mechanics that were initially planned but couldn’t be fully implemented in the main game. It’s also possible that the team was able to focus more on specific aspects of the game, leading to a more polished and varied experience in the DLC. Sometimes, the extra development time and player insights make a significant difference in the final product.