it should have waited 30 day's before you had to pick.
Yes, from a certain point of view - it makes sense for them to only ask you for payment details towards the end of your 30 days. I totally agree.
But I understand why it's done this way. There's some people here who barely even realise you're required to pay a monthly sub. So when you register the game account, it makes it clear there and then that there's a monthly fee involved. It prompts you at that point.
Sure, the more friendly way would be to have an option...'register payment details later'. But I suspect they want your card on record for other reasons. Perhaps so they can be sure you're a human being, and not a gold-spammer bot.
Anyway, the game won't charge you when you register your account. You still get your 30 days free.
If you don't want to plug in your credit card details, you can always grab a demo card number off the web somewhere; there are test numbers that exist for this purpose.