Are there that many people who will to travel by train, on an already overcrowded line through Newbury?
No, but the few there are are rich and influential, and would quite happily pay a premium rate fare. Marlborough is after all an extremely affluent area.
Compare this to another Wiltshire town, one which includes recognised areas of social deprivation - let's use Melksham as an example. Now which one suddenly looks the more likely to receive massive investment in it's rail infrastructure (at public expense)?
Cynical? Moi?