As a parent and Delaware resident, the reason it is so difficult to find a hotel room is Fair Hill, Maryland (located 10 min away) has their Five star Equestrian event and it is International. Worldwide there is only seven venues and two in the US and it is a big deal.
It brings over 35k people from all over the world to compete and attend, to the area. They have booked up all the hotel rooms, being the closest location to the event with accommodations.
The U of De needs to take this into consideration when planning next year Parents weekend.