http://www.pcgamer.com/some-destiny-2-endgame-activities-now-require-the-dlc-to-access/

With the release of Destiny 2's first DLC expansion, Curse of Osiris, the power level cap has been raised from 305 to 335, which means some endgame challenges formerly reserved for players near the 300 level cap are now reserved for players near the new level cap. Without spending $20 on the DLC, vanilla Destiny 2 players cannot level their guardians beyond 305, locking out the Prestige, or hard modes, of the Leviathan raid and weekly Nightfall strikes. 

Why is this a problem? It's the latest in a string of baffling design decisions and a failure to acknowledge them that has the hobbyist playerbase up in arms. Players who don't have the money to spend, or just don't have interest in the DLC, but still play regularly looking to maximise the challenge have now missed their window of opportunity to do so. In a move more aligned with how subscription-based MMOs update, Bungie has scaled up its endgame activities across the board, effectively removing a higher difficulty option altogether for anyone still sitting on the original release.