It's a theme in the UK. The whole analysis process is known broken. It's all built on the remains of the 1960s/70s "close all the railways" stuff for the same reason a road is an "investment" and public transport is not.
Same happened with the borders railway - over 20% over the forecast 6 months from launch
Ebbw Vale line was allegedly marginal - it beat predictions by 100% in the first year, and they had to add extra carriages the year after launch and then double track it.
