I agree they couldn’t have done it the same way, but there were options.
They could have set a minimum stay requirement. If you had to stay four or five nights instead of one, they could have spread the reservations out more.
They could also have done it by resort level. They could have said only deluxe get a reservation or only deluxe and moderate.
It’s not that they couldn’t have set up a reservation system, but it appears they decided that wasn’t the way they wanted to handle it. Aside from the chance their website will be overwhelmed a few times, doing the previews is low risk for them, even if it is nerve wracking for the rest of us.