Board Thread:Speculation House/@comment-30994843-20170109010227/@comment-25122143-20170414202538

Actually, as I understand it, Kylo got a perfectly good crystal, but he was so forceful in imposing his will on it that it cracked, and the crossguard serves as a vent of sorts, with the extra blades being a byproduct of it. That's also why the blade has a different effect than any other Lightsaber. The Crossguard wasn't an intentional design choice on Kylo's part, but he had to do it for his Lightsaber to work, so he figured "Eh, might as well make some use out of them."