Considering how evidently low the budgets for the last-gen versions of MUA2 were, it doesn't surprise me that they would try to cut down on costs by blatantly reusing a ton of assets from the first game. Heck, when characters jump, the grunts for the MUA1 voice actors still play in spite of hiring new actors to voice many of them!
But I suppose to Activision, it only served as a means for some quick cash from stragglers who still hadn't jumped ship to the newer consoles of the time.