Meant to add-
Perhaps the reason why nobody has quoted M@W's chorus vocal melody and turned it into a hit song, thereby exploiting their creativity, is that it "obviously" has copyright protection. M@W have benefited from the copyright system implicitly. Such cases are going to keep being tested. As autoharpbob says: this is the law we live by.
Of course, we could always return to the economies and values of pre-industrial societies, where exchange value was worked out informally.
Once a tune was performed, it was like a bird taking wing: it flew away, you couldn't cage it. Like a Kookaburra, that melody would fly away and sit on a branch in people's minds.