Every sunday hundreds of people drive from all over Austria to visit the zoo in Schönbrunn. They take the car because the train is way too expensive. If taking the train was cheaper then some of those people would take the train.
Yes, for each of those families it's just one trip. But in aggregate it's also a lot of people.
Why is it more important to get one person to use public transport for 500 trips rather than getting 500 people to use public transport for one trip?