Because it's pointless, it's going to shave off what...30 mins travel time between London and Birmingham?
It's going to cost LOADS, this money can be used to improve our current networks and trains.
Yes, it willl create jobs for the people having to build it, which guess what, funnily enough they need paying too.
Just meh.
Just time, no increased capacity or any other benefits then? i think you need to think about it more.
Upgrade existing network, that's already happening and cost loads. Restricted by the line we already have with no land to expand and often building built upto the boundary line. Meaning you can't do much.