Why do antlers fall of and horns dont?

The term antler is most often used to refer to the horns of members of the deer family Cervidae.

This is a bit of a stretch, but I am going to guess that the term is an abbreviation of "ante-occular" meaning "behind the eyes", since this is where the horns of these animals originate as opposed to (more or less) "beside the eyes" as is the case with the bovines, Bovidae.

Also, the deer family have solid horns, whereas the bovines have hollow horns. Perhaps the different names are simply meant to distinguish one type of horn from the other.