I think the answer has to do with the user's voice and a sense of ownership:
1. Even if spam accounts sign up, their comments and posts rarely get to the top of the algorithm because user's have a voice in the matter (downvote low quality content, and upvote other higher quality content).
2. There is a sense of ownership on the part of the mods... people who are generally passionate about the area of interest in which they moderate. There have been a number of cases over the years where moderators were acting in bad faith and the users have voiced their concerns to the Admins, who frequently remove mods or even whole subs that are operating against the benefit of the community.
I think the answer has to do with the user's voice and a sense of ownership:
1. Even if spam accounts sign up, their comments and posts rarely get to the top of the algorithm because user's have a voice in the matter (downvote low quality content, and upvote other higher quality content).
2. There is a sense of ownership on the part of the mods... people who are generally passionate about the area of interest in which they moderate. There have been a number of cases over the years where moderators were acting in bad faith and the users have voiced their concerns to the Admins, who frequently remove mods or even whole subs that are operating against the benefit of the community.