Google this and you will find that the common denominator is that no matter how big a family gets, if they just depend on their own gene-pool, they are bound to fail. In the larger scheme of things, families – even good ones – can and do produce morons.
They fail, because they disregard everyone’s advice and put those morons in places of authority – just because they are family members.
The second reason you will find in your search, is that because they stuff their kith and kin in their boards so much that they dilute their board’s effectively, resulting in weak infrastructure that directly affects decision making.
Those who survive, on the other hand, are inevitably led by those who have the required cojones to stand up to familial and peer pressures and follow their longer term vision resolutely, without succumbing to mediocre decisions made for momentary or egotistical gains.
You will find that those people have no fear in sharing their authority and trusting even “outsiders” to run their show based on ability, rather than proximity of blood-lines.