Because a lot of Dutch people don't have a creditcard or doen't use PayPal.. I think it would be extremely usefull for spotify to add the 'iDeal' online payment system for users from the Netherlands! When this payment system is intergrated to pay for Spotify Premium etc, i think loads of Dutch people will get Spotify Premium! 
I am still waiting for this myself! Who's with me? 
2014-12-04
We're happy to say this is now implemented for our users in the Netherlands. You can read more about iDEAL right here. Keep the feedback coming guys!