When SE changes something they change it based on player numbers and forum responses. When 3.0 BRD was released it got an insane amount of hate, hug not only that, it got a huge drop in people playing the job. Yoshida explained this as one of the reasons pushing him to finally change it after 2 years.
The problem with SMN is that despite the amount of people who dislike SMN right now(a small amount) SMN still remained the most popular job in the game just a few months past based off of the spring census. So numbers aren't on your side. Plus the changes people want require a full overhaul from the ground up. Why overhaul the most popular job because a select few don't like it?