I need a reason to complete challenges after completing the battle pass. I enjoy having a set of daily tasks to do to keep me logging in every day, I just need to have the "doing this makes bar go up" to make it not feel pointless. Camo farming is nice, but it's more of a long term goal and short term goals are what keep me logging in daily. You could either have the battle pass levels keep going with no reward outside of being able to see the level for each season somewhere on your account, or have the challenges award a small bit of XP for career level.