Ahhh the "Ancient Woodland" argument, much as I oppose HS2 this is not true and that can be found on t`interweb.
"As a result of design refinement, the whole HS2 route from London to Leeds and Manchester will impact on less than 0.01 per cent – of the UK’s ancient woodland.
The proposed Lower Thames Crossing motorway will impact on about as much ancient woodland as HS2 (54 hectares versus 58 hectares), yet it is only 14 miles long, compared to HS2’s 470 miles."
The "why" it is being built is to take high speed trains OFF of local networks, ergo it doesn`t need to connect cities and towns.
By segregating high speed trains onto their own line, the current mixture of slow and fast services that actually constrain capacity is stopped.
That allows the remaining services to bunch up more closely together.
This enables a doubling or tripling of capacity for the remaining services.
So you get a more frequent local service to an HS2 station and then whizz off to where ever.......... or work from home on super fast fibre!!!