Because lemmy users tend to be tech literate millennials or older, who were using the internet before it became a widely popular and used thing.
We remember a time before emojis. And to us, there is art, and more meaning in continuing the old ways of using textual symbols in clever ways to convey an emotion.
Emojis are a cop out, a cheap and easy way to do the same, invented for a mass audience that didnt want to do any thinking or be clever in any kind of way and wanted it all handed to them.
I realize this may sound silly but I will die on this hill: emojis are for children and the technically illiterate, they are an appropriation of a culture spawned by some gen x and mostly millennials when the curious of us forged our own way onto what was at one point in time a frontier of seemingly infinite possibility.