Evening flights...even redeyes...have their allure for some. But when I watch seatmaps, Florida in particular has a heavy morning bias. Afternoon flights, especially after maybe 3-4pm or so, are often dogs except at peak times.

Phoenix and Vegas don't seem as bad, and PHX in particular sometimes for YX had better loads on the 1:25pm versus the 7:10am, which always kind of surprised me. My only guess is that is partly due to the time change and partly due to the type of travelers:

Flights to Florida lose an hour, so unless you go in the earlier morning you arrive in the afternoon. And plenty of families head down to see Mickey or the grandparents on tighter timeframes and tighter budgets.

Flights to Phoenix and Vegas gain two hours, so there's less reason for a leisure traveler to get up early for a 7:00am flight so they can land in Phoenix before 9:00am. Phoenix has plenty of retirees and winter-home people, and Vegas is a 24-hour city. So going in the afternoon doesn't necessarily "waste" a day like it does to Florida.

Obviously those are sweeping generalizations, but I think the psychology kind of fits a lot of travelers.