And those passengers who would have considered using the train to go on holiday will decide to take the car instead (or even fly if flying is an option [i.e. if they live on a bus route which serves the airport]). They simply won't trust the railway.
Already has happened for a couple at work who had booked to use the trains to travel to Edinburgh next month (one way via WCML, the other via ECML), they have cancelled the train tickets due to the risk of future strikes and instead booked flights.
I've cancelled any plans of using the train for leisure over the summer, unless it's a last minute decision to go somewhere on the day/that week and the trains are running, I just won't risk it.