Why should someone who books a ticket to go and see something leave early, thus missing what they went to see? May as well stay at home!
And who pays £11 and then hopes to 'bag' a free cab ride home, as if a ride in a cab is something special. Quite possibly a driver in a car that has 'overdue service' on the display, speeding and talking on his mobile at the same time. I think I'd rather take the train given a choice!
Also, changing trains and messing around having to go and find people to speak to, being concerned that someone will stop you and say 'not a valid ticket' and try and make you buy a new ticket, as well as having to now write in and make a claim - isn't something people generally do lightly. Far more people will actually suffer all that hassle and then, the next day, wake up and think 'no more' and not even put in the claim.
I've not made a claim for anything in years, as I can't be bothered for a voucher for a few quid, so I am sure many other people think the same. I bet they never get claims from everyone on a train that is entitled to claim - even if they stand on the platform handing out forms as some TOCs do.