Mascon basins on the Moon are large craters that display significant positive free-air and Bouguer gravity anomalies. An important question is why is not every large crater a mascon, as less than half have been previously determined to be. We detrend the free-air, topographic, and Bouguer gravity anomalies and find that most large basins (28 of 41) display mascon characteristics (e.g., strong positive Bouguer anomalies narrower than the surface rims). Negative free-air gravity annuli surrounding the central highs generally are absent in the Bouguer gravity, implicating surface topography. We propose that beneath a forming large basin, the relatively narrow transient crater drives mantle uplift, while upward and inward collapse forms the surface topography. Furthermore, the nonmascon basins are all ancient and heavily degraded, indicating a postimpact evolutionary process. Our results suggest that mascon formation is the standard for large impacts on the Moon and by extension on other terrestrial planets.