History of Europe

Why do ideological third parties tend to be more successful than single-issue parties?

This is generally not the case. Single-issue parties tend to be more successful than ideological third parties as they can more easily attract voters from across the political spectrum who care about that one issue. Ideological third parties tend to appeal to a narrower band of voters who share their particular ideological convictions, making it more difficult for them to gain traction and become successful at the polls.