We don't know exactly, but recently Pinterest updated its Acceptable Use Policy last week, where now they condemn users who pay others to follow them or re-pin their images. In other words, users can't buy new followers or shares anymore. That make us question if some fashion brands actually buy others in order to increase likes and followers.
The change does not mean Pinterest users can't make money working with brands. A brand could pay an individual to create a board on its account, and that user could receive commission from affiliate Pinterest partners if his pins led to sales. The new rule only prohibits users receive payment just for pinning.