"Fate keeps on happening"—as witnessed by the current spate of "slut shaming." Women back in those days were generally required to be tightly corseted, buttoned, and covered up to a fare-thee-well, which probably is also why the word "loose" has come to refer to women who color outside the lines, as it were. But seeing this picture of a 19th-century model en déshabillé persuades me that "loose hair" was also a signifier of such fallen status. It's like the old stereotype of a (seemingly sexless, old-maid) librarian with her hair wrapped up in a tight bun. However, just like librarians can be sexy, a hair bun can come loose. And our budget-cutting losers in Washington had better watch out or a loose horde of librarians (otherwise known as a "shush") may be loosed on their sorry asses.
(Model with hair loose, between 1895 and 1910, from Wikimedia Commons.)