I think you'll find that it is because of the availability of hospitality tickets i.e. the restaurant will be open. Priced at £70 for non season ticket holders and £50 for those willing to upgrade from their normal season ticket.
The food is nothing to get excited about but, you do get a programme, tea/coffee at half time (in the warmth of the Manor lounge) a team sheet and can take a seat in block 12 behind the directors box. Value for money? Make your own minds up.