Question

Why are third parties called "minor" parties ?

Answer 1

mostly because the two most famous parties(major parties) (democrat and republican) are voted for or chosen the most, parties after that rarely get recognition, or attention making them minor parties.

but this answer is based off of party recognition.

Answer 2

Third parties are called "minor" parties because most of them are younger than the major (Republicans and Democrats) and have fewer supporters.

They also rarely won elections

hope this helps