And I'm sure NIMBY-ism and gold plating have played their part. I am in no doubt we NEED HS2, all the way to Lancaster and maybe beyond, and a branch to Nottingham, Sheffield, Leeds and York. However did we need one designed to be as fast as HS2 was? Does a small congested country need the fastest conventional railway in the world? I really don't think so.
The thing with the Eastern arm is that a chunk of the distance (from London to the HS2 junction for it) would be shattered with other services, so the costs of that are shared between 17tph, so an uplift from 300kph running to 400kph alignments (but chiefly not running speeds) is going to be insignificant per train over a 60 year period.
From that junction to the stations served it's a different matter, as there's fewer trains. However, we're still taking about a lifetime of at least 60 years (and even then it's difficult to justify the benefits over such long timelines).
Also, unless building 2 railways of 140mph (given the number of people who call for line speed improvements to the ECML to this, it's not unreasonable to assume that 140mph should be the design speed vs 125mph) works out cheaper than HS2 (remembering the second line would need a new route into London and that's the very costly bit), the theory of building one very fast line rather than 2 fast lines makes sense.
Especially given that two lines wouldn't have provided the links to Birmingham which HS2 provides (so even if the two lines are a little cheaper they may still not be better value).
Given the fiasco of east-west rail, which I'm surprised isn't in the national conscious, Wouldn't surprise me to see an empty HS2 run with staff trains only for years
As I understand it part of the issue is DDO being proposed for East West Rail (even though the head of RSSB has said that the evidence is that it's safer, although he also said that wasn't to say that there wasn't a role for a second person on the train - that's not a cue to start a debate about it, just stating that the organisation responsible for rail safety has made their position clear) I'm not sure that HS2 would be looking to do that.
However, even if they are and it does result in further delays, 10 years after opening such things would likely be forgotten by most people.