Actually, a very good thread.  The reality is no one outside the sport knows of its existence.  As a result, we get the kids of kids of kids of former horsemen.  The depth of the human talent pool is rather shallow, and there is no one standing in line to take the place of someone that isn't cutting it.  Instead, they stay in the game and add no value. 

And the irony is, many of the people listed are sub-par good drivers.  There are hundreds of others that simply aren't at all good, and could be replaced by millions of other individuals.