The railcard is a promotion to get (generally) 1/3 off some types of rail fares. If travelling is a regular activity, e.g. as with a season ticket, the traveller just needs to do the same thing every day, i.e. carry a credit card sized document or as is being suggested, their ever-present mobile phone. With season tickets, there are procedures for those that fail to do so, including when it is stolen or lost. For casual travellers on railcard discounted fares, there is still a need to carry a ticket to travel so why would the additional deadweight of a railcard present so many problems. If they fail to bring the tickets with them there are penalties, although they are sometimes waived by obliging the passenger to present the card within a limited period after.
If the rules allow more than one 'railcard' to be carried, and the passenger is one of those who are so careless (or 'forgetful') to have one on themselves, they can carry two, - or three etc., providing the sheer weight of all those cards stuck to various parts of their body or concealed within their clothing isn't too much for them to walk, - although maybe that extra weight might jog their memory.
I'm amazed that there are so many apologists for those that find the simple rules of a) buying and b) carrying the necessary travel documents, too difficult or inconvenient for them. There are nearly 10 million ENCTS passholders in England and most of them manage without problems or complaint despite that demographic probably having a greater proportion of citizens with memory and/or physical difficulties.