They should have done this for the new weapon skins featured in the Limited Edition req pack that cost 80000 req points or 9.99 in US dollars.
ODST: For SMG and pistol as ODST members mostly used the silenced SMG
Noble Team: DMR and pistol, as Noble team is from Halo: Reach and that game brought the DMR
Blue Team: Good at where its at because Chief uses the AR and Pistol.
Fireteam Osiris: Battle Rifle and Pistol as Locke favorite loadout is this.
Sharktooth: Idc
UNSC: Looks good 
343 skins: They can do whatever they want.
Spirit of Fire: I’m not sure about…
But I get it, they wanted to show it off for the HWC finals so make it AR and Magnum as it is the standard loadout of Arena and to make money.