I think the '20s connection, I suspect via pulp fiction and writers like Hammett, may be key.

Don't forget the jazz-age, silent film vamp. I am not sure if the two terms are synonymous, but Theda Bara has to be in the DNA of this archetype somewhere.

[edit] yet another trope subverted by Jessica Rabbit.

Very much so. Now I have "Why Don't You Do Right?" stuck in my head again.