Maybe because heroes are dynamic, and solve things through action? Maybe because comics are a visual medium and a physical fighter is more fun to draw and look at? Maybe because fans were apt to question how she could be so poor in combat situations and yet remain alive and with the team, when logically one of those would have to give --just like they did with Doug? If you recall, he was killed by popular demand.
And as I pointed out, the character was motivated by a desire to stop being helpless and become a warrior, like those around her she admired so much. She was motivated by a desire to stand against a nightmare of a man who'd nearly killed her more than once, and by a fear of becoming a casualty of battle like Doug. And in her circumstances, who could blame her?
If those aren't good enough reasons, I don't know what to tell you.