I'm not sure Fark is the best example, given that their demographic seems to be middle-aged folks (or at least older than the Millennial age range). You can't really (or simply shouldn't) do sweeping design changes if your demographic is aging. Every time I wander over to that site, it becomes very clear that a lot of the users are at least a decade older than me (likely in their 40s and 50s).

If it were a tech site, that's one thing, but Fark is more of a site for just anyone. Targeting that wider demo is going to attract less tech-minded and likely less-adaptable users compared to, say, a similar site where the userbase throws around a lot of lingo.

reddit on the other hand can more or less assume that the users that stick around will figure out the new site. They're probably right, or at least not horribly wrong, and are instead banking on retaining just a majority of users, not all of them.