The responsibility remains with the passenger to seek the conductor and NOT vice versa.
Really?
So take the south wales valley lines, where a large number of the stops do not have any means of buying a ticket.
Are you really suggesting that a train full of passengers should all approach the guard at the same time in an attempt to buy a ticket?
Or, is it more sensible to do what
ATW▸ actually do, and just have the guard walking through the train selling tickets, and also have an excess fares window at Cardiff Central (and staff with ticket machines at Pontypridd and a couple of other barriered stations).
The same can be said for stations across Devon and Cornwall, where a large number of them do not offer ticket buying facilities.
(now, I know the above is not the case for the actual event that happened, but I am simply questioning your logic there).