It goes like this:
The Piccadilly Line was overcrowded. The Victoria Line was built to relieve it.
The Central Line and Paddington are overcrowded. Crossrail 1 will be built to relieve them.
Victoria and Kings Cross are overcrowded. Crossrail 2 will be built to relieve them.
In areas that have no lines or stations there are no overcrowded lines or stations. Therefore we do not need to build new lines to relieve the overcrowding there...
The result of this logic is "concentration":- of resources, investment and opportunities and, naturally, further overcrowding! Central London stations become more overcrowded, overconnected, overblown, as more lines join them up.
Reaching underserved neighbourhoods first has the more pleasing effect of "distribution".