I think a lot of parents just can't bring themselves to be "cruel" enough to teach their kids the very, very hard lessons they need to learn. Even if it's the only way to save the kid's life.
Plus it's true that Lionel has seemed more into his career and not a very good disciplinarian. And re: her mother, who knows what goes through these people's heads and why they haven't intervened? Is it a different set of rules altogether because they're obscenely rich?