If a player routinely loses to some opponent... then suddenly wins using the same deck, I'd say the player must have gotten extremely lucky. Why give an extra reward for that? They already get electrum, spins, and the satisfaction of overcoming a personal struggle. Whereas if the player though of a new tactic to use against the opponent and won because of that then isn't winning more often good enough of a reward?
In the second case an extra reward might be deserved, but the AI wouldn't be able to distinguish between the two cases anyway.