Given that there are actually multiple other platforms where this feature exists and is used, it seems that many disagree with your claim about what has been “shown.”
Facebook, Insta, TikTok, Pinterest, Twitter… these are all single-site socials. None of us can do our own Facebook; the scale is part of what makes it what it is. But that’s not the niche occupied by a forum software like Discourse.
Discourse is a platform for people to set up their own spaces. It’s not like Facebook, it’s like Slack. And it’s like Discord. Both of which allow multiple reactions, and the feature is well-used.
Discord is the fastest-growing in the category, by far. So much so, that there have been active debates about how to stem the tide of people abandoning forums for Discord, including here on Meta:
The addition of Chat on Discourse is a response to one aspect of Discord/Slack that was missing on Discourse… using multiple emoji is another.
Tl;dr: I’m not saying Discourse must implement this or lose the great war… I just think the “it’s useless and nobody does it” argument doesn’t hold up and should not be part of the decision-making process.