My understanding is that it was communicated, both officially and unofficially, at that time that the journey time improvements which the Department has been very keen on for some years are not deliverable without sacrifices by many stakeholders, especially any rail users to and from Northallerton, Alnmouth and Bewick-upon-Tweed. Notably a good portion of which users would actually be part of the Conservative target voter or existing base, but of course that's nowt to do with Network Rail.
The changes likely would have been deliverable if the timetable had sacrificed those stakeholder interests, but of course that's not really the play here. They're not deliverable while trying to preserve a decent service on all of those intermediate flows.