I believe you, and I can't explain why it did work for English speakers and not for the French ones. Maybe I'm wrong in my hypothesis by the way, that's just how I feel it. Follower does not bear this pejorative meaning for French people.

Maybe Twitter did push for this word in English and it worked? And then people who translated Twitter's interface in French and decided to leave follower "untranslated" actually sealed the destiny of this word in the French language?

Although it can have that connotation in English, it has to be activated by context: “Jim is not a leader, he’s a follower”. But in phrases like “a follower of the Chicago school of economics” it’s neutral. Maybe in French the negative connotation is more tightly bound to the word.

Interesting. No, indeed, we can't use suiveur neutrally like this in French as far as I know.

We'd probably say un étudiant or une étudiante (a student) in this specific case. Or un membre (a member).

But we actually can follow a lesson (suivre un cours) without it being pejorative, so while the noun is probably always pejorative, the verb is generally not if not activated by context, as you say.