Even Walt himself said that
Disneyland would never be finished. With few exceptions, I'm a strong advocate of keeping the Disney parks fresh and new. Unfortunately that means losing some old favorites in the process.
When Epcot's Lights of Winter were retired, it paved the way for the impressive "icicle" lighting on Cinderella Castle.
Retiring the Osborne Lights is undoubtedly linked to the refresh of Hollywood Studios. Disney releases how important the holiday season is to its guests. I'll be shocked if this retirement doesn't lead to a new elaborate display or holiday feature elsewhere on WDW property.