Because prescriptivists take what has been established in the past as "correct now", completely ignoring that prescriptivists then also thought that way and considered those changes stupid.

Language evolves. We're currently observing a semantic shift of 'literally' away from its "established" meaning. We just still have narrowminded prescriptivists that believe in a "correct" language :^ )

It's literally insane how people want to be oh so liberal, but you cannot say 'could care less' or 'literally' in their new uses without those "liberal" people going mad about you not adhering to the rules. Language is one of the least consistent things we have, yet THAT's what you care about so much?

Just check out what happened to some words, and you see no one complain about them now