For whom are these for? Anyone that loved KOF is really clinging to the past still to have to use these as emojis. I fucking LOVED kof. Had every single one on AES for God's sake. And I wouldn't be caught dead using these. Furthermore, certain things simply do not go hand in hand. Like, when are they gonna come out with a Lavern and Shirley video game? What's that? Those two things don't go together? You're RIGHT.
Upon further inspection, it looks like they're not for KOF98 specifically, but an online game called KOF98 Online (Chinese title is 拳皇98终极之战OL, if anyone cares to look more into it) which came out two years ago. It's probably developed by Tencent, and since Tencent owns QQ (the social media with the emojis) then yeah.
To go deeper into your question though, I remember my first few months here. I'd see Paris-Dakar rally stickers on cars, girls wearing Arale hats (from the Dr. Slump manga), Biohazard Umbrella stickers on cars...I learned quickly that Chinese, in fact, didn't care about that stuff. They weren't rally racing fans, they had NO clue wtf Arale was, and had never played a Resident Evil game. It was just all for 'fashion'. Fuck, this past year I've seen tons of people wearing Simpsons t-shirts, Nirvana t-shirts, Linkin Park shirts, etc and they've never seen the Simpsons or have listened to Nirvana or Linkin Park. Again, just for 'fashion' - I guess kinda how weeaboos used to wear Japanese t-shirts in middle school back in America.
So people might use these emojis without even knowing what KOF98 is, beyond just some Tencent phone game. They might be surprised it was originally an arcade game developed by Japanese devils near 20 years ago.
So there's my explanation.