Many train tickets in Europe are available exclusively online. In other cases the online price is lower. So to chase up why this happens, I found the following law:

Article 11 Availability of tickets and reservations

1. Railway undertakings, ticket vendors and tour operators shall offer tickets and, where available, through-tickets and reservations.
2. Without prejudice to paragraphs 3 and 4, railway undertakings shall sell, either directly or through ticket vendors or tour operators, tickets to passengers via at least one of the following means of sale: (a) ticket offices, other points of sale or ticketing machines; (b) telephone, the internet or any other widely available information technology; (c) on board trains. The competent authorities, as defined in point (b) of Article 2 of Regulation (EC) No 1370/2007, may require railway undertakings to offer tickets for services provided under public service contracts via more than one means of sale.

Key wording: “at least ONE of the following means of sale”

Since it’s easiest to sell tickets online, they are effectively encouraging train ticket vendors to marginalise offline people and unbanked people. Further down the statute it says people with disabilities get an exceptional option to buy tickets on the train at no extra cost if there is no ticket office or machine. But no one else is entitled to that option.