Unless Mars also bought the Tribune from Zell it doesn't even have control of the naming rights to Wrigley Field so they couldn't possible sell what they don't own. Even if ownership hadn't changed to Mars Wrigley Co. wasn't likely to start paying the Tribune or ISFA to keep naming rights.
........With Mars now owning the lot of the Lakeshore Athletic club though it will be interesting to know what in the heck Mars intends to do with it (but that is another subject).