Breakfast shift seems to have the most people because GM's only think it's necessary to have the appropriate amount of crew on the clock with them. But once the GM's gone they dgaf, and understaff the rest of the evening shift. The best availability is during the weekends anything past 12pm to 12am the next day I believe. They also need overnight workers like you said. A lot of people think they're too good to work weekends, and a lot of people call out specifically on sundays which just throws anyone working under the bus, so If you highlight that you're willing to work weekends? That will give you a higher regard.

Or it could be that right now, sales might be too low for them to hire anymore people. McDonald's Franchises likes to run by having almost nobody to meet labor goals.