There are a few well known cases of large realms being split upon inheritance, but how common was that?

I've been playing a lot of Crusader Kings 3 (a strategy/role-playing game set in medieval europe/asia/africa), in which almost all realms (except those with elected rulers such as the Holy Roman Empire) always split between all eligible heirs of a ruler when he died. But if that was realistic, all realms which don't expand constantly would be split into lots of tiny bits within just a few generations. Is that how it was historically, or was the splitting of realms upon inheritance much more rare than it is in that game? Or is there another reason?