I think you're missing the point - journey numbers have indeed more than doubled but you're confusing two issues - reliability, capacity, cleanliness, customer service etc have nowhere near kept pace - the usage of something increasing doesn't necessarily indicate that it's the "best" option, for a large number of people it has been, and remains, the only option...
I certainly agree with that part of your post in respect of journeys increasing into London being driven by people being prepared to sacrifice more of their day commuting because of being effectively priced out of living anywhere near central London. The train is indeed usually the only realistic choice.
However, long distance and rural routes have also seen very large increases at off-peak times (indeed
IIRC▸ they were two markets that still grew in the last set of results when South East commuter journeys fell back) often in places where the population has risen very little if at all. They are journeys where there are usually other options available.
There are also massive success stories even within London such as London Overground which gets ever more popular and busy all day.
It's quite a complicated picture as usual.
