I think one problem is that non-regular passenegrs don't know about the short platforms in Cornwall.  I was on the down Riviera a couple of weeks ago - in coach H at the back - and the PA^▸ (Public Address) was very quiet.  The Train Manager didn't walk down the train after Plymouth and relied on a a sinlge announcement over the PA before each station.  There were 2 businessmen going to Redruth who didn't hear the PA about walking forward to coaches A-F (or whatever), and it was only because another passenger who saw them standing in the vestibule in coach H got up and advised them to walk forward that they did so.

I'm not condoning pulling the cord for a missed stop -after all St Erth is only 3 minutes after Hayle - but maybe the TM^‡(resolve) could have done more to prevent the siutaion arising.