Formicarium Challenge Army Ants

In Formicarium Challenge 3 the enemy colony has Eciton minors and majors. Why does the player's colony only get one caste from the species it replicates?
The player's colony only get the caste with special ability for variety. Army ant minors have about the same stats as black ant soldiers, they don't have special ability so it's kind of redundance if we have both.