And it was killed because no one used it correctly and it made things more difficult versus a simple like/dislike?
What makes things different now?
What's different now is the visual representation - reactions as emoji.
And speaking from experience (the TapestryMaker social network platform has had emoji-based reactions for a couple years) it really does change the quality of the discussion. Especially on phones, one-click responses are a lot easier; so giving people a big one-click vocabulary makes conversation much richer. And having it representable visually rather than textually changes the image/text balance which for many people really improves their overall experience -- even though people who prefer text may not see it that way.
Oh, and people would use those things 'correctly', it's just too embarrassing sometimes. A simple 'like' is much more diplomatic.
This was pretty much the case Zuckerberg presented for redesigning the button.