I think the reason for it is because this is what Final Fantasy games often try to do. Through their adventure they enter doubts and depressions and question the meaning of life and what they are fighting for, and Yoshi-P wanted to take that from the Final Fantasy games and do it in all this game's expansions as well.

Apparently EW resonated a lot with people suffering from depression who had not benefitted from any other sort of therapies, so it was a good thing for that reason alone.

The expansions can do this sort of thing whilst still having proper character development because it happened in some of the old final fantasy games. If they tackle depression, they can just do it in a way where the depression affects a particular character such as Thancred and watching him go through this whole period of depression and then come out of it and overcome the last boss with you.