Originally Posted by
me4yankees
I would guess this is because historically, some routes sell more last minute F seats than others, so they hold back more seats back for sale on those routes.
Possibly, but it was the DCA-PHL route (only mainline flight of the day) that cleared while PHL-SJU (more of a leisure route) won't clear. They usually have to OP-UP people on that route. My guess is they just don't care about selling F on the short flight.