There seems to be a common theme on this forum of some members promoting the re-opening of missing sections of former through routes that were initially built by competing rail companies to provide alternative links in the railway's heyday in the last half of the 19th century. These competing routes were typically closed as duplicate lines in the latter part of the 1960s, as through traffic could easily be accommodated on other more useful routes that were retained. There may be a good case for re-opening the ends of these routes where circumstances are appropriate, as these are typically links into sizeable cities or conurbations, and in some instances this has occurred. However, the business cases for re-opening the middle sections, often through sparsely populated countryside, are poor.
The former Midland Railway's route into Manchester from its headquarters in Derby is a good example. There is a very poor case for re-opening the closed Matlock-Great Rocks junction section, but the sections south of Matlock and beyond Great Rocks have been retained and used for a variety of purposes, with the South District line re-opened as a Metrolink route. Similar re-openings that the usual suspects widely promote are the Waverley line south of Hawick, Okehampton-Tavistock, Skipton-Colne, Ripon-Northallerton, Beverley-York, the Great Central line north of Calvert and the Woodhead line east of Hadfield. I would put Bedford-Cambridge in this category, although others disagree, and re-opening this section does have some political support despite a poor BCR.