A proposal for a project is not the go ahead and a go ahead is not spades in the ground. I think you'll find that they went in because it made Johnson look good in the short term and got out of hand from there. It doesn't look good though when Spain can build several hundred KMS of high speed line and Britain can't. I wonder if Boris's brexit has something to do with it.
Sure - but all the earliest steps are essential for a project to be realised and completed. Actually HS2 is a project with cross-party support, but you are correct that we, in the UK, seem to take far too long to actually deliver projects of this type. I think there are many reasons for this and I suspect that the whole grid lock over brexit where nothing else seemed to get done was a factor.
But this UK issue has been going on for decades - remember the years when the channel tunnel had opening and trains whizzed through France on high speed lines and then trundled through Kent on commuter lines and then crawled through south London to Waterloo behind suburban commuter trains.