"Pffft.... something about it being unfair to let him go because he's a ghost and wouldn't know what else to do with the rest of his afterlife, blah, blah, blah! So, what? You're going to show compassion to a ghost, while ignoring the education of hundreds and thousands of children? Why, I bet Binns isn't even paid! Maybe that's why he keeps him! What does a ghost need with money? Then the Board of Education saves on the budget!"
Florean paused to sulk. "It's not right. Even if I wasn't hoping to be hired for the position, I'd be upset."
[ooc: there may be another reason that Dumbledore didn't hire him, I don't know... but this is what Dumbledore told Florean]