> The rail network in the UK is publicly-owned, what is private is the franchise to operate on a certain route. The lack of investment, if any exists, has come from the govt
It would be the same story if it were the government operating the trains and private company maintaining the network: of course you're not going to get one organisation to put in more effort when it's a different organisation that sees the benefits. The big success story of privatisation is Chiltern, where there was a long-term arrangement with a single operator that took responsibility for the integrated system of trains, stations and so on. (Though it's notably also one of the few cases where there was real competition between rail lines).
> London and the area around me isn't getting enough, this is also false, London receives obscene amounts of investment relative to the rest of the UK
A smaller proportion of London tax revenue is reinvested there than anywhere else, and projects with a lower objective outside London BCR get funded while higher BCR projects in London get delayed.
> The main constituency for subsidising the travel costs of wealthy commuters is...wealthy commuters. I am not sure why that idea is inherently attractive (and again, it is worth mentioning...our safety record is best in Europe, there is no real difference in punctuality, our fares are marginally higher but the ecosystem we have is far more robust).
The amount of public subsidy going on rail is trivial compared to the amount of public subsidy that explicitly or implicitly goes to roads (such as the huge amount of public land taken out of productive use), and that's even more biased towards the wealthy and carries much bigger negative externalities (pollution, much worse safety record).
> The cost of a fiber roll-out for the whole of the UK is less than the Elizabeth line.
No it isn't, you're comparing the concrete realised costs of Crossrail with the made-up estimates for fiber rollout.
> The problem is that this has no end because the more infrastructure you build, the more agglomeration, the more infrastructure...London had this problem in the late 19th century with slums, the solution wasn't more density
Density is the solution; it's the reason why London is so much more productive and ends up subsidising the rest of the country.