I just wanna know why we have mechanically interesting classes like BLM and RDM who have a specific playstyle for people and they don't change despite people wanting them to be something they aren't, yet classes like SB SCH/AST/BRD changed in ways the original fanbase disliked.

They had audiences and people who like that playstyle. Why in the world would you change them into something they dislike instead of taking the foundation you had and giving QoL fixes?