A whole heap of issues
El Reg has documented many of the issues withe the ESN which show why it's just not going to happen, but the tube has some very special problems,
The chief one, and one no-one likes to talk about, is the working practices.
Say a light bulb needs replacing, and all the requisite permissions and forms have been filled in for a new one.
Someone needs to fit the new bulb. That needs to be done outside operating hours at k'ching overtime.
That someone also needs to have the necessary safety certificates. There are two of them. But no-one who changes light bulbs has either of them so has to be accompanied by someone who does.
No-one has both certificates so the bulb-changer has to be accompanied by two people with certificates. All at k'ching rates.
On the London Underground it really does take three men to change a light buld.
But it gets worse. Under the working practices they don't just rock up at the faulty bulb. The get paid to travel to a muster point and then paid to travel to the faulty bulb whereupon they take a break. Then the tricky technical work of replacing the bulb is done, then they take another break. Then they travel back to the muster point and then home.
The cost of the operation is eleven times what you would expect.
The Tetra system on the Underground is called the Connect project. It was a three year project which took more than 11 years to complete.
I am overwhelmed with admiration for Virgin media who got wifi into the stations, but hugely pessimistic that anything will happen with the ESN.