How Skippy joined the crew...through Prowl who is too shameful to return to Earth to take him back. Oh, and the ship used up its required energy for hyperdrive to fly the fuck out Earth's galaxy and it needs time to recover or some bullshit like that.
He doesn't. None of the bots know the cat is a pet with a name. Prowl tries to think of names, but in the long run, Skippy the cat goes by a bunch of different names over the course of the series; most of which will come from Wreck-Gar.