Official website of Titanfall appeared a press release announcing the release of the DLC Expedition on Xbox 360 in June, unlike the PC and Xbox versions, One which will gain access to add-on by the end of May. The reason would be dictated by different programming cycles to which the Respawn and Bluepoint face in order to develop the best versions of the game.

Specifically, the text states: "Respawn Entertainment team must first finish and consolidating the improvements for Xbox and PC, while a second time Bluepoint will devote himself to also update the Xbox 360 version. We are working together to Respawn and Bluepoint to speed up the process and minimize the gap between two release dates, so as to allow the publication of updates to Xbox 360 as closest as possible to the release of those being worked at Respawn. [...] The first DLC for Titanfall, or Expedition, will arrive on Xbox and PC in may, while the Xbox 360 will be available in June.

Remember that Expedition is the first of 3 DLC intended to enrich the leisure offer of Titanfall, and contains three new playable maps: Runoff, Swamplands and Wargames.