Burke isn't getting a great deal of game time because, whilst Hasenhuttl rates his ability and physical attributes, he doesn't feel that his tactical discipline is there yet. And for a team that plays a high pressing game, that's a pretty key part of an attackers game.
Also, it'd be harsh to drop any of Poulsen, Werner, Forsberg or Sabitzer from the starting XI as they're all in good form at present and Leipzig went joint top of the league yesterday. Very much a case of 'if it ain't broke, don't fix it'.