Yui isn't a fairy here lmao, they never went to ALO, remember XD? As for why, reminder, this Yui was basically reborn/rewritten with a made-up past where she was witnessing Asuna being a slut constantly desiring Inoda's cock behind Kirito's back and cheating on the latter for it, so it's only natural she wants him almost immediately. She's more of an OC with the same name than Sinon, and just barely less so than Alice and Administrator (Just by sharing the same origin story as her canon self).
It was a mix of how Fujino rewrote her and how he had to switch the focus to go mostly back to Inoda and Asuna with the quarantine and everything, I'm afraid. Her new character required a slower and more focused plot for her to get what she wanted, but she suffered from both being a side-character and from her plot being less connected to the main one than Alice's, then further from Sinon being made more important plot-wise thanks to becoming part of the council while she ended up as her lackey. Until this new Gigachad Kirito route opened up she actually had sadly fewer chances for more H-scenes thanks to her role in the plot and how she was the only one taking things 'slow' (Everyone else was forcing, or trying to, conscious Kirito one way or another, but Fujino decided that her, despite having been raping him in her sleep, actually didn't wanna 'push him too hard' when he was awake, lmao, otherwise if she had really forced the issue they would almsot without a doubt ended up fucking back during the bathtub paizuri scene).
Now that there is a route where a part of Kirito actually wants her openly, she has more chances to shine, but Fujino is also having to write the plot for 2 different routes so is not gonna be fast, there is a reason why this update once again seems to have exclusively Asuna scenes despite Kyouko showing up again after so long and with a new look, after all :O