Something unique to duels is duel level. A draw allows both players to preserve their current duel level. This is consequential if only because the AI gets progressively more challenging (i.e., more available mana) as your duel level increases. If you haven’t faced duel level 11+ AI wizard in Chaos mode, then trust me you’ll be grateful to have draws… and 20 turns will feel like an eternity… if you face an AI opponent with lots of extra mana with which they fuel their mega spells and talismans. The only way I made it to Chaos Duel level 27 was because I managed a couple of draws against some really high level AIs.
Also, why is there a need to change the turn limit in the duel mode? That’s a big can o’ worms to open. The whole purpose of duels is to limit play-option choices as much as possible to maximize the chances that players can face players rather than an AI. The more options to play, then the more fragmented the already fragmented playerbase becomes and the more likely you’ll face an AI no matter how many players are dueling.
Admittedly, fragmenting the playerbase is not such a big deal these days. But Snapshot would have to feel very charitable to devote more dev time to consequential feature changes which are not part of steps to increase the playerbase size and thus hopefully sales.