Error with Custom Maps/Gametypes

Okay so I need some help here. As an experienced forger and someone who vastly enjoys custom games I’ve encountered a slight error. When I make or load up a custom map in Halo 2 Anniversary custom games however I’m only able to choose from 3 gamemodes along with all of their variants. That being (Slayer, Juggernaut, and Infection), This really ticks me off because I’ve made several maps specifically for playing Oddball, CTF, and Assault gametypes, but I can’t seem to load them up with anything but the default maps.