Great Crossbows have the highest base damage of any weapon. That means they do the most damage.
Repeaters? When you get doubleshot, the repeater splits it up between three strikes. Psh, wimpy.
When Great Crossbows get doubleshot, people just get hit twice. The bolt explodes and deals twice as much damage.
Wielding a Great Crossbow gives you +50 to Charisma. Nothing else does that, you sexy beast.
Great Crossbows straight up knock peeps over when you roll a 20, which will be all the flippen time. The force of your awesome hits them straight in the face and they just fall right down. No save. You don't have time for that bull.
Great Crossbows get so many damage options, like going 18 Rogue for a +1 to critical multiplier. That means when you hit a monster in it's vitals, not only does the bolt explode- but the explosion explodes. Three times as much damage. You monster.
Great Crossbows can automatically bleed out your extremely unworthy foes. Hitting something with your greatsword? It doesn't bleed. Wimp. Cut something with your dagger? Not able to pierce it's skin.
Get a better weapon. Great Crossbow. Manly. Awesome.