Not that this helps but car rental places are like trailer/truck rentals. A particular location will often just be a franchise and own their own vehicles. They'

Not that this helps but car rental places are like trailer/truck rentals. A particular location will often just be a franchise and own their own vehicles. They'll also handle vehicles from other locations/corporate but they have their own little fleet. They charge one-way rentals based on the likelihood of that vehicle returning to them in some time frame and/or them getting a replacement vehicle while the one-way is rented. More generally they schedule based on their return schedules. If they have a car scheduled to return at noon and you set your pickup time to one, they assume they'll have that car and be able to rent it to you. If I don't drop it off at noon they can't assume I'll drop it off at 12:01 so they need to let you know it won't be available (since they can't predict my actions). This is all compounded by agents on the lot renting out cars under the radar or booking agents doing some customer service override. They are incentivized to rent cars, not rent to specific people. For them it doesn't matter if your car is unavailable, it got rented out which made them money. Good luck getting a car and making your drive.