Just a few possible valid reasons: • They never planned for it and it's not a high priority, high impact service to provide, so they aren't making plans for it either. • Like with many other games, PlayStation may be refusing to support it. • PlayStation exclusive politics. Could be stipulated in the contract with PS, could be technically difficult to separate what exclusives people can/can't access if they cross platform families, syncing progress and console switch-backs would have too many problems, could break all kinds of account syncing to the website and companion app, or could have been decided as too much trouble and effort to bother for more than one reason. Its not so simple as just "don't copy exclusives over to Xbox". • Bungie didn't have enough time during D1 production to put in place all the necessary means to support cross-platform, so they took it off the table. • Just because something can be done by somebody else doesn't mean it's the same situation for another. Bungie's game engine is different, it's production schedule is different, its priorities are different, its developers are different, etc. No two games can be exactly alike in the ways people want them to be.