You're making the failed assumption that everyone has countless hours to play a game. Some people log in for 10-30 minutes a day if that to play. Some people prefer only PvE where they can pick up materials as they go. If someone is only spending their few minutes of play doing PvE, there really isn't any time to do PvP so preference is really on trading the materials that they have rather than burning up time doing PvP. Especially when a good materials route can net you a bunch of materials while you also complete bounties, public events, and do other things simultaneously.