In the past, we saw Halo games get slapped with purchasable map pack DLCs, but Halo 5: Guardians took a different approach. Instead of offering map pack DLC for players to buy, they offered them for free and shoved microtransactions into the game that allowed players to purchase REQ packs.
While microtransactions are annoying, it sounds like they helped preserve Halo 5's community.
According to Analyst Micahel Pachter, the reasoning behind going to microtransactions for some items and offering free DLC packs was because every time they did DLC paid, they'd lose part of their player base – which means fewer people buying their DLC and fewer players in general. This new method of asking for people to buy the skins and armor they wanted, while handing out free DLC, allowed 343 Industries to maintain their player base.
Additionally, the cumulative spending in microtransactions on Halo 5 for that six months was greater than all DLC sales for any Halo game ever. Though it should be noted that this means the microtransactions sales outweighed any other Halo's DLC, not the cumulative sales of all the DLC for all the Halo games.
With this success, it's safe to say 343 Industries will turn around and apply the same method to Halo 6.