Because the War of Wrath is just so big and involves, like....just so many people and stuff, we should, like....find a way to kill loads of them real quick.
Maybe we could send in an army of ghouls?
Also, scrap Morgoth. I mean, what's the point? Everyone knows Sauron and he was around at that time anyhow so.....
And also, this whole jewel thing. People found it hard to imagine first time around when everyone was fighting over a ring. They won't accept another film like this. Is there any way that all these guys could just ignore the jewels and fight over something else? Luthien, obviously....
Ignore every other female character, they would detract from Luthien.