Dear little bow-wow

While I was out yesterday, I saw a dog running around on the beach while its owners looked on. The animal then bit a seagull very badly. The owners smartly tethered the animal and then walked off. The seagull was unable to move for some time, but moved with difficulty when another dog ran towards it.
Why are idiots like these people allowed to be in charge of an animal? Why are dogs allowed on the beach?
I don't get it.