After all, if you forget your Tesco clubcard you receive good customer service (bring your receipt in next time for your points to be added)
That's a poor comparison. There's no potential loss to Tesco in that scenario. There is in the example in the OP. A better comparison would be "If I forget to pay for my £100 worth of shopping in Tesco, then eat all the food, they will allow me to pay within the week".
if you forget or loose theatre tickets they can be looked up on the database and be reprinted
Because theatre tickets are valid in the booked seat only. Ticket holders on a train can sit anywhere, in effect. It would not be possible to discern if someone is "trying it on", whereas the theatre can do that quite easily by seeing if the seats are still unoccupied.
Theatres also don't provide an essential public service that suffers from pernicious fraud from a section of its users.
if you don't have your driving licence when stopped by the police you can produce it within 14 days
Don't really see how the police provide "customer service"!
The police, if you don't do that, will send the boys round and knock on your door. The police can arrest and detain you, and they know where you live, and they will come and find you. It's easy for them to enforce.
I understand the point you try to make, and I wouldn't agree that the railways are a bastion of fantastic customer care. I think, however, we should be realistic with how the railways can practicably deal with members of the public who appear to have not paid the proper fare.