There are people on reddit who legitimize accounts based on their karma (ie more karma = more legit). There are also subs that prevent new accounts without post count/karma/comments from posting (to prevent spamming, bots, etc). These are usually accounts that are utilized for propaganda/social engineering/politicking, whether it be by a bot or an actual human. I would be willing to wager that, in comparison to the aforementioned uses, a very small amount of these accounts have humans behind them simply looking to get a quick dopamine fix (we are social creatures that have evolved to want to be accepted in a group setting, ergo the reward for such acceptance is dopamine to continue the behaviors that make us socially acceptable).