I get that in general we don't want to be asking chess related questions here, but occasionally a meta question or answer can be illuminated with an example where the replayer or just a diagram displayer would be useful.
2 Answers
Because we (the ♦ moderator team) haven't asked for it yet. I was planning to do so, but then 'other things' happened and I decided not to bother the Community Managers right now.
It would be especially useful for a Sandbox question where users can test the syntax, or to provide a network-intern replayer for chess questions on Puzzling.
Well, it does now. :D Thanks to a note from Glorfindel, you'll find that the replayer has now been activated on Chess Meta so, enjoy!
Thanks to Yaakov for actually making the necessary changes for this!