That's comparing the very cheapest advance bus fare to the walk up fare for the train. I'm sure Michael O'Leary would be proud
Using Cork as an example, you could make the same argument for travel to Dublin City Centre, yet 2.5 million use the train between the two cities every year, so if the option is there, plenty will use it. Of course, Cork has the advantage of a pretty fast train service to Dublin that beats the bus by 45 minutes. I doubt the numbers would hold up for other lines.