But public money...
The one glaring difference between public transport and the other privatisations is the need for subsidy.
Whatever else might be beneficial about the dynamics of private ownership how does it make sense to put public money into an industry that pays dividends to private investors?
It's easy to accuse SNCF and DB of not being particularly well run but there is a basic political consensus that transport is a public good provided at public expense to the benefit of all — even those who never use it benefit from the positive effect on the economy over all.
The logic of privatisation should demand that transport becomes self-supporting yet there is also a wide understanding that to be so the already expensive fare structure would have to become prohibitive for many. Beyond the direct cash it is inconceivable that an entirely unsubsidised industry could make infrastructure investment such as Crossrail.
When you look more broadly at pressures of profit, investment and the public good the example of the water companies is clearly picked to make a point. A counter-example might be the economically vital roll out of fast broadband, something that profitable VM and BT wouldn't undertake without the government providing £2bn subsidy (and still fails to mandate fibre to the premises).
Not everything is rosy in the world of privatisation.