Why does kafka choose a cockroach rather than any other insect or animal

Because when you think of the most disgusting, hated insects ... a cockroach is one of the first ones that comes to mind. Kafka wanted you to know exactly how he felt ... hated, alone, disgusting.

the use of an insect is particularly significant because of all the things in this world, the insect is often seen as bothersome, disgusting, and easily squashed. While some people may see value in insects (for pollination, for example), most find them easy to ignore or horrific.