Zero availability but looks empty?
 

I am trying to make a reservation on ual.com. I cannot choose the flights that fits my schedule (leaves after 6pm, direct flights) because the website says, "the selected flights do not have the requested number of selected seats available in the specified service class. please revise your entry." However, from the seat map, the flights look pretty empty. The "availability" from the flight info was indeed 0 in all classes for these two flights. These flights are almost a month away, can they be all sold out?

Seat maps are meaningless when determing loads. Many people may have seats but no seat assignments. This is especially prevalent when there have been schedule/equipment changes and everyone loses their seat assignments.

If availability is zero, you can't buy seats. It may be sold out, or they be anticipating canceling the flight, or any of a number of other reasons.

Might be a tour group. How are the loads for other flights that day or the same flight on other days?

Other flights that day are fine, and the same flights on other days are available as well. I guess I'll have to take the next day's early flight out. (AA's late evening flights are full for the day as well.)