42K is low but the product appeals to a very small segment of consumers: Snapchat users, who don't wear prescription eyeglasses, who happen to have a face shape complimented by the single size/style of Spectacles.
Selling prescription eye wear in the United States seems to come with a lot of red tape. I don't think they want to get in the business of requesting and verifying an eye exam within the last 12 months before selling a one size fits all consumer item.
Do you really have to to just provide frames though? Couldn't they just sell empty frames and have optometrists install and request lenses. I think that's how most frames work now.