The Netherlands is in the EU. English is the most widely spoken language in the EU, even after the UK left, because it is by far the most common second language. Nearly half of the people in the EU can speak it.

In Northern Europe the percentage is even higher. In the Netherlands there are almost as many people who speak it as there are Dutch speakers.

Taking into account people from other EU countries who are there on business plus tourists there is a good chance that if only one language was to be used for train announcements more people on the train would understand if it was in English then if it was in Dutch.

Yes, I'm obviously not mad with them using their own language, and I am studying it since I live there. But it's in the EU, and there is a lot of international tourists on the train, who shouldn't be expected to learn the national language of every country they visit just to navigate it.