[YoshiRulz]

Most of the platforms you mention are "replacements" which have "won" over a long term—Google unseated AltaVista and Yahoo!, Reddit outlived Digg and SlashDot, and microblogging like Twitter started as blogs. And of course, Fandom "replaced" other, less bad wiki farms by virtue of buying them.

[AlienRobot]

But I don't personally remember any of that happening. I wasn't using Reddit when Digg was still around, just like I didn't join Facebook when MySpace was still relevant. The first time I used Yahoo! was after its search engine because Bing with a different label.