Why do political scientists argue that minor party successes lead immediately to
failure?
The major parties control the election process and make it difficult for minor
parties to participate in campaign events or even get their candidates on the
ballot.
Minor parties have trouble raising money. In order to raise money they have to
compete by copying the major parties.
Minor parties get only a few percent of the votes in most elections.
As soon as a minor party becomes popular enough to threaten the major parties,
one or both major parties will adopt the minor party's positions.