On the one hand, these fanatics, throwball-throwers and other recently added npcs at least provide the illusion the game has a lot of players in it. On the other, they're frightfully toxic and the repetitive messages get old fast.
We had something similar to this not too long ago - Circus barkers, which only situated at a couple of spots and weren't half as annoying. Jagex removed them; not sure whether it was because people found them annoying, or simply to declutter the game of non-essential stuff. Whatever reason they did that must certainly apply to the Bane Fanatics and co.
They won't even be a novelty once the rework hits and you start seeing people wearing actual Bane (even if just cosmetically) so there will be even less reason to keep them then.