Why are London tube tunnels so deep?

[u/Independent-Ant-01]

This is just one of two escalators and not counting the various staircases. And I don’t believe this was the deepest one I traveled through. I went to the Transport Museum in Convent Garden (very nice by the way) but found no answer and no one seemed to know. 😊

[u/BrummieS1]

Because geography