It increased when ranks were wiped out and players can go in freely without worry of losing their rank and getting matches quicker. In a ranked playlist, match waiting is longer by finding similar players and with party restrictions in play.
Halo 3's BTB went unranked not even a year after launch. Halo: Reach's BTB was unranked from the get-go and it was always in the mix of the upper populated playlists with Infection and Team Slayer. Halo 4 it was similar.
Seeing Objectives pretty much ignored in these new playlists isn't much of a surprise. In Reach when Bungie handed over the playlists, 343 added Flag Slayer to Team Objective for pete's sake; they heavily decreased the weighting for Flag and Assault in Big Team. In Halo 4 they were pushing Oddball and King of the Hill as individual playlists, and quite frankly, they weren't very popular. I mean, of course they won't. You don't put Oddball on every single small or midsize map. It's not balanced, nor fun.