This sounds like it surely is some kind of discovered political law. if you want your party to grow, broaden it, leave the grass roots, alienate the original founders. If you want your party to fight for the original ideals, it will remain small.
A beautiful example of this can be seen in the swedish nationalist party. In the beginning they were fiercly anti-immigration, and anti-EU. It took them at least a decade, or maybe it was 2, to reach about 4% and enter the parliament.
