Vespa
Established Member
It is a marketing tool to sell capacity that would otherwise be empty, pure and simple. By tailoring a number of cards to specific groups of passengers with different validity restrictions, the demand can be directed to very specific services. As far as the railway is concerned it isn't broken so it doesn't need fixing, only a few tweaks maybe.
As Bletchlylite said
I think I'd answer that "but simplicity is a strong benefit in and of itself".
With so many different railcards it can be an administrative nightmare and confusing to passengers, they would be put off so if you make it simple and easy to understand, there would be a better take up of the service.