Primarily I think because idea of a cold sandwich and miserable side snack fills me with revulsion, which is only compounded by adding a dismal lukewarm fizzy drink. Obviously I could get something less dreadful from the station, but it wouldn't be hot by the time I was halfway through the journey, and would likely still be too bready to count as much of a meal. All of this I can only do if I get on at a station with facilities and have time during my connection to do the buying.
I think most of all though, I don't want to. They've already laid out the train with bare metal seats, requiring people to bring along a cushion, so the inconvenience of not letting me get food either is really just going to stop me travelling at all, or drive me into the open arms of Flybe.
