It's because Obama was never an admirer of Lincoln in the first place. Lincoln was just another disposable prop in the grand illusion.
True. Anybody with an Illinois connection who runs for president is going to play the Lincoln card no matter what they actually think or how they actually feel.
Plus, it gives reporters something to write about -- either on their own (because Lincoln is someone everyone knows at least a little about), or with a little guidance by the Obama team.