the tube needs this so badly because the station bank for the northern line got so much sharp curves, in fact its so curved that they even gotta spam a announcement that says "Mind the gap,"
Sam Sitar when a train stops, the gap filler extension signal detects the train. Only then it extends the after that gives the signal to the operator/train controller to open its doors. when it’s moving back to the tunnel, the gap fillers retract back to its original position. It can’t retract after the train leaves though.
On virtually all lines that were built later, station platforms were straight, or if there was a curve, it was so gradual that gap fillers weren't needed.
When that station opened in 1904, the cars were shorter, the trains were shorter and only had vestibule doors for entry and exit. The whole thing was VERY different.
have you ever put a straight object next to a rounded edge? if so you would know why there are huge gaps. also some trains stop at different points of the station because no train driver is perfect, so having platforms aligned with exits of the train would be a bad idea.
