Because if not that then it seems the real reason to play Curse of Obsession is to curse yourself and have a less killable Avaricious Dragon on your board to get some red card draw going
As for why Greasefang isnt popular in Standard, well, she dies to a LOT of things, and BRO Standard is filled with very easy, very cheap removal that many other formats dont often run as plentifully, but the reality is that there arent a ton of viable good Vehicles for her to reanimate
There is plenty of life gain not on this list that still gets some niche cube play as lifegain cards and also plenty of regular cube cube cards that get play but not really as any sort of life gain thing
Card Set(s) -BLACK Marshall.D.Teach- [ST-27] CARD VIEW ST27-005 | SR | CHARACTER Marshall.D.Teach Attribute Special Block icon 3 Type The Four Emperors/Blackbeard Pirates Effect [Activate: Main] You may rest this Character: K.O
Hakbal provides steady consistent value to your deck, and while he doesn't do anything game-breaking you're always going to be happy to cast him