Irish Rail's unfair fares

If a passenger buys a €20 Irish Rail Dublin Cork single ticket for a specific train and then decides to change the time of travel to an earlier train, Irish Rail charges a €30 surcharge. If a passenger buys a single ticket for the same journey on the internet the ticket costs €36.

Can anyone try to explain the logic of that?

It does not make sense and it is neither fair nor sensible.

Fair fares please