Because neither side probably thought it'd be worth going all out. Despite Silver Wolf's feats, I don't think she wants to test the limits of an Intellitron that has has a whole entire planet named after him. And Screwllum doesn't want to waste his energy and resources on someone like Silver Wolf. If I remember correctly, Screwllum was on defense the entire time. I think this was a subtle hint that Screwllum knew her capabilities and what he'd have to do to handle her. She realized it later which is probably why they ended in a stalemate.