are these just not a thing anymore?
I really have no idea. Sometimes Warzone Turbo is featured in the weekends, or for a week. Same goes for some Multiplayer types.
It would be really great if we had double xp ( now with double rp? ) weekends like we had in Halo 3, Bungie always featured awesome game modes with great custom made maps. Loved every single weekend of Halo 3 then.