The end of the 'dynasty' as John saw it?

John Prescotts son David has lost the selection to be the next MP for the Hull East constituency, beaten by Karl Turner. Why, if Prescott had been such a good MP and saviour to the local area was his son turned down? This was to have been Johns icing on the cake as he rumbled off on the Euro gravy train of 'retirement' when he finishes at the start of the next election. What on earth has prompted the labour party to slap them down like this?