Earlier quoted context omitted.
According to Reddit's user agreement, you own content you submit, but you give Reddit a "do whatever you want with it, even to make money off of it" license. https://www.reddit.com/help/useragreement#p_17
Is it me or this is stupid? I mean, this is the digital world, you can make as many copies as you want, so if you give them a licence to whatever they want with it, what are your options after submitting something?
Licensing doesn't just mean making an exact copy.
Let's say Reddit was the one that packaged up a story posted on /r/nosleep/ and sold film rights—the user who posted that stuff would have an uphill battle to get anything from Reddit's profits on the arrangement.
But, as a user, you can still make your own deals (you still own and can license the content yourself to others), and you probably can only make that deal because of Reddit exposure.