it was a phase? a fad? the cool thing to have? everyone else had one. Short answer:I don't know.
In my opinion the same reason Megatron is NOT a gun anymore. Don't want little Johnny to have a sword cause he might stab someone
Lightsaber. Sure it's a dangerous weapon even though as the movies go along there's ways to counter them. Why? they made it so cool looking. The things that can be done with it.