The reason the Marston Vale is "underused" is because it doesn't actually serve anywhere - and extending it to MKC would make precious little difference to that.
Let's look at each of the stations in turn:
Fenny Stratford - for many people Bletchley is just as close and serves more destinations (with apologies to Darlo Rich)
Bow Brickhill - if you're heading to the centre of MK a car or taxi will quicker and more convenient.
The same is true of Woburn Sands and Apsley Guise.
Ridgmont only really serves the Amazon and other warehouses.
Lidlington - serves the village but that's only 1300 people, unlikely to use it more even if the train did run to CMK.
Millbrook, Stewartby and Kempston Hardwick are all in the middle of nowhere.
Bedford St Johns - serves an area of Bedford, but I doubt running through to MKC would generate additional traffic.
Of the 4 stations which are more or less in MK - Fenny Stratford, Bow Brickhill, Woburn Sands and Apsley Guise - only one really serves an area of employment - Bow Brickhill with Caldecotte Lake Business Park next to it - there's not much in it between Bletchley and Fenny Stratford for most of the employment areas of Bletchley.
Firstly: Fenny is not just as close to bletchley for most people. It is a 20 minute walk from where I am to blethley station.
Secondly research the users group carried out has shown the lack of a link to mk is retarding numbers. We dont need a curve to satisfy that demand- a reversal of the exisitng service will do
Thirdly there are plans for vast numbers of houses along the line. Plans yes but devlopment is begining. Several thousands homes are going in at the bottom of Fenny Statford already and work on the new distrobution centre development has started next to Bow Brickhill station that will fill up the gap between the a5 and bow brickhill station.
Sewartby is supposed to have the vast brickworks site redeveloped for housing. Kemspton is supposed to be some kind of new village. That changes those locations vastly.
There is a market there that will only get bigger but the speed and unreliabilty of the service kill off demand. The blidy 230's will get the line closed!
I am sure you know best about all this mind. I mean i only live here and rely on the train so i know nowt!
Oh yes, it's usage had more or less doubled between 2016 and 2019 - what would be interesting to know is where the people who were using it were heading.
My bet is towards Bedford - easier that trying to drive through and park in Bedford.
There is a collage there as well. That (and Bletchely collage) is the key factor in determining the current service levels
Well that is straying into politics again. It is the excuse that is always made. I repeat myself from above " where there is a will there is a way".
There is no will and therefore no way. Also refusing to acknowledge the importance of "politics" is indicative. That is the key not something to dismiss.