Because on live BM can spam absorb shields. Forget about it in Legion where mitigations and heals become much more handy. You will use Effuse during leveling, in battlegrounds, in arenas, while soloing elites and old content, even doing random dungeons. Especially if healing is more efficient thanks to traits.
As for immolation. It was just random idea but I personally would trade minor dmg on self for additional decent AOE any day. Particularly for monk who can mitigate this damage and heal through it. And particularly applied to Breath of Fire, that isnt part of core rotation and used specifically for dealing AOE on packs