The problem that's at-least-purporting-to-address is one facing all the levels of government: boomers promised themselves future taxpayers would give them lots of services (money) while setting aside wholly insufficient capacity to make it fair to the future working citizens.

Since lockdowns I think the underground only recovers around 70% of its operating costs. Maybe you have seen different figures?

The freezes eliminated investment projects needed to keep pace with population growth. There's also just big problems maintaining the stations and doing more than the bare minimum needed to keep the lights on. Travel on it and the stations are dirty, overly hot, etc.

Drivers on London's roads are very heavily taxed already, supposedly to reflect those externalities. Public transport obviously also contributes to pollution and congestion, especially when building underground lines, it's not externality-free.

I don't think TfL has a cost crisis. Crossrail overran but that was mostly due to the software complexities of the signalling tech debt around the Heathrow tunnels and other issues that can affect any kind of project. It's just hard to tell right now because they can't build at all.

The fare freeze was broken by central government briefly, but only by bribing Khan with central government money for upgrades. Exactly the outcome he wanted!

The difficulty of getting people to vote for tax rises is a good justification for privatization. This difficulty isn't some uniquely right wing thing. The Democrats and Labour don't campaign on general tax rises either. At most, the left are willing to campaign on "tax rises for people who aren't you". That's because any party that wants to raise taxes on the majority loses.

So, governments of any color have to work with that as a constraint. Given that nobody has worked out how to convince everyone to accept big increases to their tax bills, you can either pay for new expenditures with borrowing or with cuts elsewhere. Sometimes cutting elsewhere is also hard, so either:

1. Everything gets put on the credit card. This ends badly.

2. Stuff is privatized. This yields an immediate cash influx, and voters are usually happy with the results which is why very few privatizations have been rolled back. The reason is that outside of very left wing spaces most people trust private companies on pricing much more than governments. Private companies run special offers, sales, sometimes cut prices even in the face of inflation and can be visibly seen competing on price. Government owned organizations never do this.

It's also (quietly) popular with governments on both left and right for another reason - it means they have less stuff to manage and less stuff that can blow up. If there's a problem with a privatized industry they can just tell you to switch to a competitor instead of needing to campaign on it and promise to do better.

Natural monopolies do exist and sometimes governments just have to bite the bullet and run such things themselves. But there's a lot of room to debate what is and isn't a natural monopoly.

I don't think Trump is anyone's idea of a textbook conservative, especially not economically. He's a former democrat with populist instincts. Such politicians are often popular. It's frequently said in the UK that the median British voter is socially conservative and economically liberal.

It's true that the US subsidizes its road network. The effect is somewhat different though. If TfL doesn't get enough money in due to price controls then the network just degrades. If the US subsidizes its roads, the network can be maintained using subsidies. For it to be equivalent, roads would have to be privately owned but unable to charge the true cost of maintenance.