My guess: they haven't solved the "fit" problem, they won't bother trying (too hard), and it doesn't matter.
These dresses are equivalent to "found money."
Woman has a closet full of dresses. They're old, uninteresting, unwearable, etc. She posts them online, earns "buttons," and buys dresses that look like they might work. Some do, some don't. Net result: more dresses to wear.
And those that don't can just go back into the system again, too. Positives all around.
The "buttons" part is even more clever, in that they're building a real ecosystem that doesn't center on cash. Also, I can see this working incredibly well for pregnant women; they only need their maternity clothes for 5-6 months or so.
These dresses are equivalent to "found money."
Woman has a closet full of dresses. They're old, uninteresting, unwearable, etc. She posts them online, earns "buttons," and buys dresses that look like they might work. Some do, some don't. Net result: more dresses to wear.