Germany has proportional representation. It's absolutely reasonable for parties in those systems to run on small policy platforms, especially if they're not expecting to receive a large share of the vote.

The Pirate Party, if it gets into government, will invariably be a member of a coalition with limited power to influence policy. In the aftermath of elections it may have limited bargaining power as a balance of power/kingmaker party. In both of these situations it makes sense for it to be a "one-trick candidate", using its influence to deal with the issues that it cares about, and staying more or less quiet on issues that the larger parties care more about.