I really don't know why the tech is super expensive as it can be prefabbed concrete lanes and just placed on basic concrete stumps across the countryside.
Simple answer, which land are you going to put it on? Compulsory buy back? Rail reserve? Huge cost there.
which considering it would be walk on/off each end like a commuter train would kill aviation on the route.
You really think those facts have not been discussed over Cognac and Cigars the last twenty years. Certain business people lobby governments to keep high speed rail off the agenda.
In another view, look at the grief HS2 is giving the UK.