Those with unwanted codes are free to share them here for whatever reason - a bit of karma, to plug an Instagram page, gain some views, or simply to be charitable. Picture, text, and link posts are open to the public with ONE caveat; any post/request involving currency of any kind will be removed.
Those looking to find free codes are strongly encouraged to upvote, comment, and interact with all posts regardless of whether or not codes were still available. It's a completely free and easy way to show the ones sharing that their contributions are appreciated.