Kakarotto of Universe 13 never received the tutelage of Grandpa Gohan and never lost his Saiyan heritage due to never suffering severe head trauma as an infant like his Universe 18 counterpart.
Kakarotto's unhinged personality
He shows no remorse over killing millions of people and never developed any of the relationships he normally would have. Like a typical Saiyan, Kakarotto is shown to be cruel, prideful, merciless and sadistic. Due to living in solitude for the entirety of his life.