Short answer
The Stack Exchange model is based on gamification. Gamified environments typically deploy incremental rewards that tap into the brain's reward system, making these applications addictive, in a quite literal sense. In addition, reputation increases come with incremental gain of moderator abilities, which give a sense of power.
Background
The Stack Exchange environment is definitely a matter of gamification. But as you already indicate yourself, there's more to it than just reputation increase. It's the privileges and moderation tools that become incrementally available when you are climbing the ladder. These tools give users the ability to exert influence, and eventually they even allow changing the content of the site, without much restrictions.
Gamification is used in a lot of applications. Basically it taps into the reward system. The reward of providing a good answer is the incremental increase in reputation and badges. What's even better, more rep comes with step-wise increases in moderator tools on the SE network, which basically corresponds to empowerment on the site. Now all these things are powerful motivators. Neyman (2017) gives a catching account of this phenomenon:
Closely tied to variable rewards, "gamification" is defined in the tech industry as the process of using game mechanics to reward the completion of tasks. Academically, "gamification" has been defined as "a process of enhancing services with (motivational) affordances in order to invoke gameful experiences and further behavioral outcomes." Experts recommend implementing rewards in small, frequent bits so that the user of an app feels a sense of achievement. They also recommend "sharing loops" that integrate rewards with the users social network by allowing the user to share their accomplishments
Sounds eerily familiar, doesn't it?
The Stack exchange gamified environment does exactly this: the reputation increase is highly incremental. Reputation increase will give you a sense of accomplishment. With that, the reward centers will release dopamine system, as has been associated with gamified paradigms (Janssen et al., 2017). Dopamine makes you feel good (see for a review Arias-Carrión et al., (2010)). Eventually you want more and more and you might even be craving it (the constant checking out whether you have gained some reputation), akin to addiction. It's know that social media in general, such as the likes on FB comes with shots of dopamine in the reward system. Exactly this mechanism is the reason people becom eaddicted to drugs like cocaine, heroin, meth, which are all powerful dopamine releasing agents (Diana, 2011). But also alcohol, tobacco, gambling and sex release dopamine in the reward center and are therefore potentially addictive. I think that gamified activities fall into the same class of dopamine-releasing activities.
Why am I answering your question right now? Why not another one? Because I want that bounty, and the associated dopamine rush. Why did I just stop revising my paper to answer this question? Procrastination, yes, but even more importantly, it will yield a reward on the short term. The reward system is a highly ancient structure, part of our 'lizard brain'. It is highly sensitive to rewards on the short term, bypassing, even short-circuiting our cortical inhibitions that strive to achieve bigger goals that will sustain rewards and happiness on the long run.
Lastly, and already shortly hinted at, also in your post, is that reputation increases come with incremental gain of moderation tools. The ability to downvote and close questions give a sense of power, a sense of you controlling this site. An infamous study showing people's lust for power comes from the Stanford Experiment.
In this experiment, an experimental “jail” was set up in the basement of at Stanford University. The prisoners were a group of study subjects, the other half were assigned the role of guards. All subjects were males. The guards tuned from good to evil when the experiment evolved. In the end, they started punishing the prisoners, by denying them food among other quite distressing acts of bruatlity. The prisoners were even (sexually) humiliated and victimized. A lively account is given in the New Scientist (Perry, 2018). What it shows is that people love to be able to exert power over their peers. This in turn, no doubt, will also be fed by the reward system.
References
- Arias-Carrión et al., Int Arch Med (2010); 3: 24
- Diana, Front Psychiatry, (2011)
- Janssen et al., Pediatric Physical Therapy (2017); 29(1): 95-99
- Neyman, A Survey of Addictive Software Design (2017)
