They are only optional if a player is not a someone who only likes doing quests, they will need to be done in order to level up.
These bonus missions are just grinding / gathering quests used as filler XP because the dev team didn't have enough ideas / time to implement interesting quests for players. If EA still works the way it did when I worked there it is probably a time problem. These kinds of quest are dead simple to set up and don't require a lot of testing so once the main quests are put in and tested, any extra XP that will still be needed for leveling can be gained by setting up one of these generic sets of quests with the correct number of enemies to defeat.
Most other MMOs I have played do the same thing, because not only does it make filling out the extra XP dead easy for the developers, once a new major expansion comes along they will want to speed up the leveling for the lower levels, and they can easily do that by removing all the bonus quests and reducing the XP needed to level by the amount given by those quests.