The weeks leading up to Christmas are not as crowded as Christmas week. There would be tons of upset guests who would be locked out of the MK for a hard ticket event during that time. With the parks being so busy, lines get way long and the parks are open later, probably to give all the guests a better access to the attractions. Plus there usually aren't discounts, prices are higher at the resorts.
Also, New Years Eve is a blast at the parks. Crowded, but fun. MVMCP is also fun, but not like NYE.