OK HO -

I understand that this thing is entirely possible.

But WHY do we need this?

It is a huge expenditure, and only benefits those cities with enough legislative clout to get a train-stop put in. Otherwise, it only benefits LA and NY, and contrary to what these fine people may think, there are other places people live very effectively.

I think that, while it may be a really cool beans thing in terms of tech, it is a very poor use of our energy and money when the rest of the country has only a bare-bones rail system or none at all.

True it is largely for the bigger cities, at least initially, but somewhere in the Planetran article it mentioned that it moves people with sufficient energy efficiency as to reduce the overall national need for energy by between 10 and 12%.  That is not a small number.  

I suspect that, following the success in Europe it will start to be adopted here in the highly densly populated areas of the East Coast Corridor and gradualy spread outwards.

The big problem left to solve is that of digging the holes fast enough and with a low enough energy cost, and there is some work on that which might be promizing.