You will never get better by simply saying lets stop it, cancel the project and 'rethink'. Your not going to find a route that is much better. Your not going to magically find much supplier for your trains and equipment.

Also the short section that they are working on is by far the most expensive per kilometer compared to the northern parts. So the cost was always going to be pre-loaded in the early part.

Its also the case that this 3x number is not correct when you adjust for inflation. Covid and other stuff has increased because of inflation specially in that sector.

Another issue in the UK rail industry is simply that building and investing is so incredibly inconsistent that there isn't the pipeline for training people. And the constant political battle about HS2 also makes companies hesitant to do the needed investments.

But bottom line is this, unless you simply continue to work on HS2 and other infrastructure projects (like desperately needed electrification) you simply will never get better at infrastructure. And there are many things to learn and to get better at, on every level from parliament down to individual construction worker.

Unfortunately so far the 'reflection' that the UK has done on the issue with HS2 have been extremely disappointing and they have learned very little. But still even so, just by doing it the people and organization have gotten better and are moving increasingly faster.

Not doing the next parts of HS2 is hilariously stupid as the larger benefits only happen once the whole thing is complete. The UK has spend likely 50-60% of the total cost and only gets about 20% of the benefits.