I think Reddit used to be a niche site for hackers [1], hobbyists and enthusiasts. Now it's a mainstream site where regular people browse news and memes. Maybe Reddit alienated it former audience, but it doesn't mean it's dying - it just changed.
The internet used to be a place for hobbyists, hackers, and enthusiasts. That's not true anymore, at least not exclusively. But that supports your point - when the lake turns to saltwater you dont survive by being a freshwater fish.
[1] as in "hacker news"