Risen is not a killer IP. RPGs that don't differentiate themselves don't sell well. Amalur succeeded almost entirely because of that demo, word of mouth from that demo, and to a lesser extent the names attached, and even then it kept getting marred as "generic".
Witcher 2 has the social media love. It captured the eye of the internets rather perfectly. I almost think some of it is manufactured, but they have rabid fanboys in the media now. Games without that perfect storm have a hard time Getting traction.