Here's why:

* Diploid cells have two sets of chromosomes (one from each parent).

* Haploid cells have only one set of chromosomes.

Gametes (sperm and egg cells) are specialized cells that fuse together during fertilization to form a diploid zygote. If gametes were diploid, the resulting zygote would have four sets of chromosomes, leading to abnormal development.

Therefore, animal gametes are haploid to ensure that the offspring inherit one complete set of chromosomes from each parent.