343 Industries is continually making adjustments and modifications to the Halo 5 multiplayer ecosystem. It requires a lot of fine balancing work in order to ensure that it's appropriately suited for all players. Well, part of that suitability included removing two playlists from the multiplayer lineup.
According to the post over on Halo Waypoint, the reason that the two playlists Triple Team and Shotty Snipers are being replaced is because they're utilizing rotational playlists. As mentioned on the site...
We know there are players who enjoy the gameplay these two playlists offer but overall each of these hoppers attracts a tiny fraction of the online population and as a result can't really sustain a permanent position in matchmaking.
This doesn't mean niche game modes and playlists will be removed from matchmaking for good, it just means that they're being a bit more assertive with optimizing the playlists to give players both unique gameplay experiences in the Halo 5 online arena, and also limit the amount of esoteric options so that only a few people will enjoy the online experience.
For instance, during this most recent rotational playlist 343 is re-implementing Assault into the fold. The standalone mode will be part of the matchmaking experience and is a vanilla 5v5 setup for the most recent "seasonal" refresh.
Take note that the rotational playlists are exactly what they are: rotational. It's mentioned on the Waypoint site that these matchmaking changes will not be permanent for Halo 5's online multiplayer, but will instead attempt to cater to the varied tastes of the Halo multiplayer community.
So does this mean that we'll eventually see Triple Team and Shotty Sniper make a return once more? Possibly. Do we know when? Absolutely not.
343 Industries has been using the same update and content roll-out method that Ubisoft has been using for Rainbow Six: Siege. Both studios are focused on getting out as much free content as possible while stacking the cash shop stores with lots of cosmetic goods or character customization options in order to keep gamers playing and luring them into spending more on the titles. In the case of Halo 5 that would be the Req packs. In the case of Rainbow Six: Siege that would be the operators.
Halo 5's multiplayer has received a lot of praise, especially for the Warzone mode, which is a very cool new addition to the online PvPvE setup, but the single-player portion of the game left a lot to be desired. For Halo 6 at least they know where they've gone right with multiplayer, so they won't have to do much in that department. But they'll definitely need to work on the story a bit more if they hope to bring the series back up to the mainstream sector where its as buzzworthy as the older titles that Bungie used to develop for Microsoft.
In the meantime, you can continue to check out the multiplayer offerings of Halo 5. 343 will soon be rolling out a Team Doubles refresh for the rotational playlist in celebration of Valentine's Day.