OTAs (online travel agencies) like Expedia have contracted prices with hotels and most hotels only issue contract rates for a limited future time period. So OTAs limit future date bookings to whatever time period they have contract rates for. As different contracts have different time periods, not every hotel will be bookable during the window offered on the OTA's booking form, returning a no rooms available response.
Hotels may accept a direct booking request that far in advance, especially for a major event like an eclipse. The downside is that they may not guarantee a rate at this point in time, but merely pencil you in for that date. Then later when they decide how much they are going to gouge travelers, tell you the actual price. Deposits, how much and if refundable are entirely up to the hotel.