Because Kuechly was a MLB in college and has the ability to run the defense in the middle. But now I realize Davis is out as well which would make that pointless.
If just Beason was out, Anderson at ROLB, Davis at LOLB and Kuechly in the middle makes sense in a game day situation.
Even if TD was playing it's not something that they would likely do in a preseason game. Preseason is about getting comfortable at your position at game speed, even if that means sending out reserves to keep people in their proper places. They wouldn't play Luke at MLB during the preseason if they weren't planning on using him there during the regular season.
If Beason were to go down during the regular season then you can expect Luke to be the slated reserve, but not during the preseason.