We haven't had a Fortnightly Topic Challenge since the Short and Sweet one, and I enjoy reading those puzzles. What happened?
Fortnightly Topic Challenges are a bit of an on-again off-again thing for this site. We don't always get them organised - it seems to be an "if someone is active and bothered enough to announce it" kind of thing.
Even back in 2015 there were big gaps: What should the subjects of our fortnightly topic challenges be? (with updates!) Eventually there was a hiatus so long that a new meta thread was started to reboot them: Fortnightly Topic Challenges Rerun! That didn't last very long, and now it seems there's been another long hiatus.