Simply common sense to combat fraud. If you are too lazy (or rushed) to spend the 5 minutes it takes using the machines to buy a ticket, or for 99.9% of travelers to check-in using your pre-paid card, that's not the NS's problem but yours.

You seem to be complaining just because you can, not because there is a terrible inconvenience. I fail to see why the ns.nl website is a pain, they even provide an English language version and everything is fairly simply. You just cannot pay with a credit card for domestic tickets because the demand isn't there. Should have been a fairly simple addition I agree and would have been nice for international travelers. But I fail to see that such a minor thing would cause a lot of people to complain like you do.

If you are a regular visitor to the Netherlands buy one of the pre-paid cards and you won't have to wait in any line (I have several of those for destinations I travel to). And if you visit infrequently the machines at all major stations will just delay you for the few minutes that it takes to buy a ticket using your foreign credit card. There's even machines when you are waiting for your luggage to arrive at Schiphol. No learning curve, any fool can operate the machine even when jet-lagged. I've managed machines in Japanese after a long flight, you should be able to select the English option and then simply choose Rotterdam since it's on the main screen as a fairly common choice.

It's still miles better than arriving in the US and having no decent rail connections available at all.