HS can't do a reservation system at this point since people have already booked their rooms and made vacation plans with the intention of visiting GE. You can't tell people, oops, you need a reservation now and you didn't get one so you can't get into GE, sorry. There are a LOT of hotels in Orlando that qualify as onsite so there would be far more guests than available slots.
HS is going to regret not doing the reservation system because it's going to be a madhouse without one, but it's too late now.