Mark Goodge wrote

arrival hadn't occurred to me. But, given that I do most of my
supermarket shopping on the way home from work (by car), it's not
unreasonable for rail commuters to want to be able to do the same
thing when arriving home by train. The obvious locations, though, for
station supermarkets would be commuter stations at the "home" end of
the route, rather than the city centre destination stations.

When I worked in Moorgate and commuted from SWT Surrey I sometimes
shopped in a nearby supermarket (then Safeways) at lunchtime or before
going home and sometimes stopped off at Clapham Junction on the way
home to visit Asda or Lidl. No M&S nearby then, but even if there had
been there wasn't much there that was worth the higher price. Also,
most SWT stations beyond Surbiton are distant from their town so 'home
end' supermarkets would have little daytime trade.

--
Mike D