For example, if you clear a mission of the scenario as a battle-type class, as an adventurer, you’ve already experienced this story. Even if you were to change your class to a Disciple of the Hand and try to experience the same story from a different angle, as an adventurer, this is just merely something that you have already accomplished previously.
Even if there are quests with different angles, such as scenario A1, scenario A2, scenario A3, they will be no different from scenario A1. It’s possible to flesh out some ideas, fix the axis of time and create "A1", "A2", and "A3" as parallel episodes. However, in this case, after clearing episode A, once you play episode B, you're already heading towards the future of the scenario and if you then play episode A2 or A3, narrative paradoxes will develop.
So, you're thinking now, "Well, how about if you create a episode A2 version 2 in case you play episode A2 after clearing episode B…" This is just not possible. For a console game, there is a finite end point so something like this is possible. You can even play again from the beginning. But for an MMO, as long as it is being updated, the "what ifs" can continue on infinitely.
The way to avoid this is to have a flag so if you don't clear A1, A2, or A3 then you will not be able to reach episode B.
However, if you set it up so A1 is the Disciple of War/Magic one, A2 is the Disciple of the Land one, and A3 is the Disciple of the Hand one, it results in you not being able to move forward unless you play as every class. Creating these types of flags ultimately results in a loss of freedom.
Well, how about if you make it so if you clear either A1, or A2, or A3 then it counts as a complete clear? Looking at this from a class standpoint this is okay. However, when looking at this from the adventurer standpoint, each class is parallel to one another. Due to this, the development team cannot guarantee that players can see every story as the class they desire to.
For MMORPGs, since data is saved on the server, it's not like you can simply hit the reset button and roll back your progress.