Honestly when It comes to Destiny lore I'm hooked, and I saw some forums where people was sayin "that wasn't crota's sword, he already has a sword". Well im gonna explain it. The "sword" Crota was wielding wasn't a sword, rather an extension of himself. The Crota we fought wasn't physical. It wasn't even spiritual, since you destroyed his soul in the wakening mission. Where you fought Crota was the only place he could exist. You fought a manifestation of Crota's essence. He couldn't bear a sword. This is where swordbearers come into play. A lot of knights use swords, but are they called Swordbearers? No. Swordbearers are Knights who bear the sword of Crota. This is why there is only 1 swordbearer at a time. Once a swordbearer dies, the sword, once realizing it isn't in the right place, returns to the hands of the next swordbearer in line.