Connie Y. answered 04/24/19
Retired credentialed high school and college English teacher
I wouldn't say this is inversion. It's creative writing that is more like a poem. The title itself refers to a "song." It's my interpretation that "they" are not lusting for dragons exactly, but lusting for their fire power. The way you re-wrote it has the wrong object for the lust by humans. If you recall, historically, when "man" discovered how to make fire, it was a big advancement for all mankind. The word "for" is often used as a synonym for "because" especially in old style writing, e.g. "...for He is the power and the glory."