Why are hypomethylating agents as single agents not approved yet by FDA for treatment of AML (technically off-label)?

DNA hypo methylation gets agents are not approved as single agents for treatment of AML as Phase 3 studies with both azacitidine and decitabine vs treating physician choice of best alternative regimens failed to meet their primary end-point of statistically significant improvement over-all survival ...

However, they are active in AML with which is hypoproliferative , but seem to have no activity in the patient with a modest to high increasing wcc. I have had several patients with low wcc and heavily infiltrated marrows have remissions or improved counts for several years