\n This will be one of the few changes the developers will be giving for select players to try out what is essentially a near-complete version of the game, as you'll get to see what some of the end-game will look like before you get to the actual ending of the game. But they're keeping it closed because they don't want to spoil it for people who want to see what it looks like as they gather feedback.
The full story of Lilith's return to Sanctuary is not something we would like to spoil prior to release—players will experience a post-campaign Sanctuary during the Closed End Game Beta. Also, for many, the end game is their favorite aspect of Diablo—we want to ensure it feels satisfying, and with no shortage of challenging variety to experience across many, many demon-slaying gaming sessions.