Kind of a tangent but Voat used to be a direct clone, though it seemed to attract more of a certain negative tone among its users that seemed to characterize the site. Culture of a site is as significant as the tech in terms of persuading/dissuading users from participating, particularly early on imo.

Reddit has its own particular, identifiable cultural aspects (some positive, some negative) though it's also large enough that it's managed to escape being pinned down to only its more negative aspects. Twitter maybe not as much among some crowds though it's still a very broad userbase.

Admin, mods and finally users set the tone of a site and lead by example. On HN for example the more one has read over time what the tone of the place is and the type of content and moderation, the likelier it will continue, almost Ship of Theseus style with regard to users.

While if this place for example were more accepting of crass comments and submissions then the culture would adapt and invite more of the same. Some might like or prefer that but it also has its downsides, particularly for users who like aspects of a site/sub-community but find other aspects more difficult to be an apologist toward.

Idk where I'm going with this apart from I wouldn't want to be in someone's shoes trying to broadly handle maintaining a decent culture that isn't weighed down/characterized only by its more negative aspects :p