Why do you think Hannibal attacked mostly city states that were by the coastline?

Because of their vulnerability.

Explanation:

Hannibal was a Carthaginian general and he is regarded as one of greatest military commanders in the history of the world. He was known to be extremely tactical, intelligent and powerful.

He attacked mostly city states that were by the coastline due to their vulnerabilities. Most cities focused on land warfare and weren't really vast in the water water war fare which he took advantage of.