I don't think there is one big reason, just several reasons. Add together the fans staying away because of the managerial appointment (how many is anyones guess) + fans staying away due to player sales/only two new signings + those on holiday, + those who didnt go because of lack of money or the kick off time or the fact it was on Sky or the fact it was the third home game of the week. It was 8,000 down on last season but that was a Sat 3pm and albeit for the wrong reasons it was a crucial game.