They're a vintage Singer, so are good machines. No worries, they will work forever if you keep them oiled, and will work almost forever if you don't. They are lightweight - good to take to a class or on a trip. They are cute. They aren't as common as some other vintage Singers, but not actually rare. So that makes them desirable (not everyone can find one they can afford). It's a combination of all the above.
bkay