Trust is only for shadowbringers (leveling?) dungeons, so there is still the daily leveling/80/expert roulettes, which will group you with other people. You only go through each dungeon once while leveling unless you're farming for gear (which won't take long either for leveling dungeons) or other drops. Then there are the trials and raids which won't have trust. So the multiplayer aspect of the game will still be there.