Alfred Hitchcock always referred to the Maguffin as the thing in a story that everybody wants. What that thing is may not be particularly important. What is important is the lengths your characters will go to in order to get that thing.
The Maltese Falcon revolves around something everyone but the central character wants. He has no interest in the falcon at all. He just feels the need to figure out why someone killed his partner to get it. Sam Spade’s motivation is honor rather than love or money and that, to some men at least, is considered romantic.
I think a lot of guys enjoy the idea that they are they martyrs of society. Could Sam Spade just forget about his partner and try to get himself a few bucks out of the Falcon? Sure he could.
But he’s working towards a higher cause. When someone kills your partner you are supposed to do something about it. You’re a man, dammit, and that’s what men do!