They never got into the Swedish parliament, only to the EU parliament.

They did not perform very well in the Swedish elections (less than 1%, 4% is limit to get seats), and after their initial push their momentum seemed to die off.

According to my personal view, a large part why the Pirate Party would not succeed in Sweden was that the party members (not the 'sign up for free on a webpage'-members, but party leaders) and their activists were very different in ideology. Party members were strongly libertarian while activists were more on the left.