Part of the reason Disney may be restricting the states is that they are trying to find out how price elastic demand is right now. Think about the comments on this thread and others.
No one is going to go to Disney with the Covid restrictions.
No one is going to go to Disney no matter the cost since the economy is in such bad shape.
More people would go to Disney if they offered a discount.
They may be exaggerations but we've heard all kinds of variations on these themes. Right now times are so different that Disney may not be able to accurately predict if or how pricing will drive bookings. This way, they get to see it in a smaller sample size. If it drives significant bookings, they can roll it out more broadly. If it doesn't, then they may not bother rolling it out. Or perhaps try a steeper discount first. Historically they have a lot of information to predict what discounts would do to existing and new reservations that may not apply right now.
We also need to keep in mind that there is a real cost to Disney since these can be applied to existing reservations. For every reservation that takes advantage of the new discount, they lose 30% (assuming it was a full rack rate reservation and not a rescheduled rate already discounted). I'm not sure what % that is, but they will definitely lose some money. They need to recover that first before they start to make money on the new reservations.
One other thought. Although I wouldn't think it would be a big driver, if there are a lot of people canceling their full price reservations, maybe this is a way to keep existing reservations from cancelling. We don't really know what Disney is seeing.
Either way, Disney seems to be taking measured conservative approaches to relaxing and expanding capacity and offering discounts and this appears to be another example. If it is successful maybe they will roll it out further. If not, they don't lose as much money.