To be fair, this was a foregone conclusion and Lucas knew it was coming. ... I am not familiar with the gaming segment of the business at all, but I do know they have struggled greatly for over a decade now.
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SirLink has the greatest degree of authority on the subject here, but I'll take a whack.
Since the late 90's, LucasArts would outsource game development for projects like Rouge Squadron(Factor 5) Knights of the Old Republic/The Old Republic (BioWare Corp.) and Battlefront (Pandemic) to name a few. LucasArts did not make many games during the 00's compared to their output in the 90's where they made more than Star Wars games, games like The Secret of Monkey Island, Day of the Tentacle, and Grim Fandango come to mind. Their recent work over the past five years has mainly been Star Wars games with an original one off game and an Indiana Jones game that was cancelled.
Two of their most recent projects illustrate mangements thinking.
The Old Republic (EA/BioWare): While not successful at first, it is doing well now and EA picked up most of the risk and budget for that project.
The Force Unleashed 2: Developed in house by LucasArts, received poor reviews and sales failed to meet their targets.
As you can tell, it does seem like the success of The Old Republic indicates why they have chosen to shut down internal projects at LucasArts.
HOWEVER, LucasArts had two VERY promising games in development
Star Wars:1313
First Assault (Storm Troopers Game)
http://kotaku.com/5990366/leaked-fo..._source=Kotaku_Facebook&utm_medium=Socialflow
Disney should have continued the mix of internal projects along with games made by others.