It looks like there are a bunch of superhero (Marvel?) skins that got the ‘lego treatement’, but you have to think of the sort of legal agreements between Microsoft and Epic. - It may have been a situation where Epic created a 3D model of a MJOLNIR armor and had to submit it for approval.
Going through that process again for Lego Chief is probably low priority. (As opposed to superhero IP holders where they can do dozens of heros at once)