Well, they're absurdly easy to accidentally maim yourself with and unless you're precognitive the blaster deflection feature is virtually useless, so just packing a gun is usually a better move. Kyber mines also didn't exist until the Empire, and they were heavily restricted with only the Emperor himself, Vader, and the Inquisitors getting any at all that weren't being sent to the Death Star. Jedi still go on a bit of a quest to find a crystal in the new continuity. And if you and the crystal don't get along for whatever reason the blade will be heavy and unwieldy. Most of the kyber crystals don't care much, but the older ones have personalities, like the one in the Darksaber.