Why is parthenogenesis common in ants ... ?

It is common in lower animals such as invertebrates and insects, bees and ants where sexual activity is not involved

Explanation:

Parthenogenesis is the reproduction of ovum without involving the sexual activity. Ants reproduce without mating. the queen ant produces fertilized eggs which develop into female ants. similarly ants lay eggs which are haploid and become males.

It is common in lower animals such as invertebrates and insects, bees and ants where sexual activity is not involved