Why do people willingly pick rifleman over observer or commander?

Recently I’ve found that the AR-7090 and the F-2000 are the best guns in the game, so I’ve been using them quite a ton. Every time I load up a game and get in, I usually try to play commander, never even thinking of playing riflemen unless all spots for observer and commander are taken. Is there something I don’t know about riflemen compared to observer and commander, or are people just stupid? And yes, I know that you need to get to a specific level to unlock commander and observer.