Network Rail estimate that there is 40% suppressed demand on our service at peak times. This means that if they ran 40% more trains they would still be as overcrowded as they are today. This is because the trains are so crowded that people use alternative methods to commute (cars, buses, cycling, etc).
This level of suppressed demand is one of the highest on Network Rail, but instead of adding more peak services to the centre of town, they are relying on the ELL to take the load, and because these are 4 carriage trains they will only increase total capacity by 25% whilst inconveniencing the majority of people who do not go to Canary Wharf or switch to the Jubilee Line. Incidentally (or possibly not), Network Rail predict 25% increase in passenger numbers over the next 10 years across the whole network, so their plans don't even touch the suppressed demand that already exists.
Overcrowding may be a fact of life but Network Rail are not meant to be making the situation worse for us!