You're not taking into account the nostalgia people have for the 121s, too. Add to that the fact they saw service across five decades and hauled every type of train on the network. Plus, they can be run in multiple with the 141/181 class.
I'm conscious this discussion is bringing the thread off-topic, and has been discussed ad nauseum elsewhere, so maybe better to discuss in one of the pre-existing threads on the matter.